Palazzo Costaguti, also known as Palazzo Patrizi Costaguti, is a mannerist architecture Roman, located at the corner of Piazza Mattei with Via della Reginella, in rione Sant’Angelo in Rome.

Large in size, it also runs along Via dei Falegnami and its rear facades are in Piazza Costaguti. Currently used as the seat of the Universitas Telematica Mercatorum.

The palace was built in the first half of the 16th century for Monsignor Constanzo Patrizi, treasurer of Pope Paul III, on the site of the demolished Church of San Leonardo de Albis, itself built on the site of an ancient Roman temple.

In 1578, with the death of Patrizi. The building was sold to Ascanio and Prospero Costaguti, members of a Ligurian banking family, for 26,000 scudi. In the early 17th century, the Costaguti family became treasurers for Pope Paul V Borghese, responsible for the construction of St. Peter's Basilica, to which the family's prelate, Cardinal Giovanni Battista Costaguti.

During this period, Costaguti renovated the building to a design by Carlo Lambardi (years 1597–1619): while the oldest wing of the building faces Via della Reginella, with a beautiful portal that was once the main entrance, a new entrance was opened in Piazza Mattei, in front of the famous Fountain of the Turtles; the façade here is attributed to Ascanio de Rossi, while the one in Piazza Costaguti is said to be by Antonio De Battistis.

In 1823, the entrance (which had become rear) was incorporated into the Ghetto of Rome and the Costaguti family closed the gateway, starting to use the portal in Piazza Mattei as their main entrance. In the course of the century, new renovations were made by Giovanni Battista Giovenale, continued when the Costaguti family merged with the Afan De Rivera, a noble family of Hispano-Napolitan origin. Since then, the building still belongs to the marquises Afan De Rivera Costaguti; the family has other properties in various parts of Italy — the most important of which is the Palazzo Costaguti in Roccalvecce, near Viterbo — and came to be related to the Florio of Sicily by marrying Giulia Florio, from their marriage a woman Costanza Afan de Rivera Costaguti was born.

During World War II, Marquis Achille Belloso Afan De Rivera, a lifelong fascist and an officer of the Militia, during the persecutions in Rome gave shelter to many Jews in his palace: during the rastrellamento del Ghetto, «in an officer's uniform, he blocked the Germans at the doorway who wanted to enter the palace», probably to capture those who had taken refuge there from the Piazza Costaguti door to exit through the other door.

The façade on Piazza Costaguti has two floors of windows, the first with architraves and triangular festoons and the second with cornices. At the eaves, with mixed lines, is a 19th-century raised floor with small balconies with iron balustrades.