Ca' Rezzonico (Italian pronunciation: [ˈka (r)retˈtsɔːniko]) is a palazzo and art museum on the Grand Canal in the Dorsoduro sestiere of Venice, Italy. It is a particularly notable example of the 18th century Venetian baroque and rococo architecture and interior decoration, and displays paintings by the leading Venetian painters of the period, including Francesco Guardi and Giambattista Tiepolo. It is a public museum dedicated to 18th-century Venice (Museo del Settecento Veneziano) and one of the 11 venues managed by the Fondazione Musei Civici di Venezia.

Ca' Rezzonico stands on the right bank of the Grand Canal of Venice, at the point where it is joined by the Rio di San Barnaba. The site was previously occupied by two houses, visible in early paintings of Venice in 1500, which a century and a half later were in a sad state of decay. They belonged to the Bon family, one of Venice's patrician clans. In 1649 the head of the family, Filippo Bon, a Procurator of the city and patron of the arts, decided to transform the two houses into a single large palazzo on the site. For this purpose he employed Baldassarre Longhena (1597-1682), the greatest proponent of Venetian Baroque, a style slowly replacing the Renaissance and Palladian architectural style. Longhena was the designer of the famous dome of the Church of Santa Maria della Salute, a Venice baroque landmark. By 1661 Longhena had combined the two earlier structures, and work had begun on the facade facing the canal, and had reached as high as the first, or Noble, floor. However, neither architect nor client was to see the completion of the Palazzo Bon: Longhena died in 1682, and Filippo Bon saw his finances ruined by the cost of the palazzo. He was forced to halt the work.

Filippo Bon died in 1712, and the unfinished palace, already decaying, was inherited by his sons and then grandsons, but none had the funds to complete the construction. In 1750 The Bons offered the unfinished palazzo to Giambattista Rezzonico, a banker and fabric merchant from Lombardy, whose family had bought a title of Venetian nobility in 1648, during the War of Candia with the Ottoman Empire, when the Venetian state coffers were depleted. Rezzonico paid 60,000 gold ducats for the unfinished building. Municipal inspectors examined the building, and concluded that most of the structure was a ruin, in danger of collapse. Only the rear part of the building, completed up to the second floor, had a roof and could be saved. Rezzonico hired the most prestigious architect of his time, Giorgio Massari (1687-1766), who had built the churches of the Jesuits and the church of the Pietà in Venice, as well as the palazzo of the Grassi family, which faced the Rezzonico palace on the other side of the Grand Canal.

The Rezzonicos rushed the reconstruction along. In 1752, the accidental dropping of a piece of marble caused the scaffolding to collapse, dropping five stonemasons to the ground below. Massari largely followed the original plan of Longhena, but made a number of modifications to suit the lighter rococo tastes. He removed some ponderous double columns on the facade replacing them with more slender pillars, and eliminated a heavy plinth of columns, giving the building a lighter, more graceful appearance. He also installed a row of small oval windows above the larger windows on the second floor, adding light and a rococo touch.

The facade was finished between 1750 and 1752. Turning his attention to the interior, Massari broke with Venetian custom and put the major ceremonial room at the back of the building, not overlooking the canal. He doubled the height of the ceiling in this room and eliminated walls to create a more dramatic space. He laid out a ceremonial route that would take visitors from the dock and gateway on the Grand Canal to a fountain in the interior courtyard, surmounted by the coat of arms of the Rezzonico in marble; then taking a triumphal hallway to the monumental stairway which took them up to the grand salon or ballroom. As soon as the salons were completed, their ceilings were painted with frescoes by Giovanni Battista Crosato and in trompe-l'œil by Girolamo Mengozzi Colonna.

The interior work was nearly finished in 1756. The pinnacle of the Rezzonico's power and the Palazzo's grandeur came in 1758, when Carlo, the younger brother of Giambattista Rezzonico, was elected Pope as Clement XIII, the same year Ludovico Rezzonico married Faustina Savorgnan, uniting the two richest families in Venice. To mark that occasion, Rezzonico commissioned the most celebrated painter of Venice, the aging Giovanni Battista Tiepolo, to paint the ceilings of two salons, along painters with Gaspare Diziani and Jacopo Guarana.

The palace was the site of further celebrations in 1759, when Aurelio Rezzonico was elected Procurator of San Marco, and in 1762, when Ludovico Rezzonico was elected to the same position. For three nights, the facades and interiors of the palace were lit with torches and candles in celebration. Upon his election as Pope, Carlo Rezzonico transferred a large part of the family art collection from Venice to Rome.

Fifty years after the completion of the palace, in 1810, the last member of the Venetian branch of the Rezzonicos, cardinal Abbondio of Pisa, died, bringing an end to the family line. The palace nearly became a Jesuit College, but went instead through several families, and in 1832 to Carlo Pindemonte, the grandson of a Piedomontese poet and political figure, Ippolito Pindemonte. Pindemonte sold all the furnishings and art collections of the palazzo. Only the frescos remained in situ. In 1837, Pindemonte sold the empty building to Count Ladislao Zelinsky, who in turn rented the palazzo to the Baron von Bülow, then to count Zichj Cerner. From 1840 to 1857, it was rented to the Duke of Modena and his family, which included Don Carlo, the Duke of Madrid, the pretender to the Spanish throne.