Uppsala Castle (Swedish: Uppsala slott) is a 16th-century royal castle in the city of Uppsala, Sweden. Throughout much of its early existence, the castle played a major role in the history of Sweden. Originally constructed in 1549, the castle has been heavily remodeled, expanded, and otherwise modified. Today the structure houses the official residence of the governor of Uppsala County, various businesses, and two museums.

Nearby Gamla Uppsala was an important religious and aristocratic center from at least the 5th century up until 1273 (when the Catholic archbishopric was moved to the area that became modern-day Uppsala). It had been at the end of the 5th century that the Yngling dynasty is known to have established themselves in Gamla Uppsala. Today, large royal burial mounds are extant and traces of ancient royal manors have been discovered at Gamla Uppsala.

In the Middle Ages a royal estate, known today as Föresäng [sv], existed in an area of Uppsala called Islandet. This estate was destroyed by fire in 1543. During the Protestant reformation, a medieval archbishop's castle, which stood west of Uppsala Cathedral (near the site of the present-day Archbishop's Palace), was confiscated by the monarchy of Sweden. Both this castle and the Föresäng estate were used as early royal residences in Uppsala.

Uppsala Castle was built during the reign of Gustav I Vasa, a period when Sweden was becoming a great power in Europe. After its initial construction, various monarchs remodelled and expanded the fortress into a representative Renaissance castle.

Following a peasant uprising against Vasa's rule, known as the Dacke War, it was decided to build new defensive castles in the kingdom, including one in Uppsala. Construction of the castle started in 1549 atop a large esker called Kasåsen. The newly constructed complex included royal apartments in the south-west corner, and two large bastions on the western side. Both of these bastions, called respectively Gräsgården and Styrbiskop, remain a feature at the castle today, although only the foundations of the original royal apartments remain (and house Vasaborgen museum). Soon after completion of the new castle, an addition to the east of the royal apartments was constructed, adding "representation premises" such as a hall of state and church. The Styrbiskop (Bishop-Controller) battery was permanently trained on Uppsala cathedral owing to the hostility between the church authorities and the king from the beginning of his reign.

During the reign of Eric XIV the representation addition was completed. Also during his reign, the Sture Murders took place in the castle.

In 1572, while John III was king of Sweden, a fire ripped through the castle heavily damaging both the original royal apartments and the representation addition. Franciscus Pahr was hired as architect to rebuild the damaged castle. Pahr envisioned a new south wing to replace the fire-damaged structure, with royal apartments in the western half and a hall of state and church in the eastern half. To the north would be a courtyard, bounded by colonnades and pillars. Pahr died in 1580, with only the western half of the south wing completed. Another architect, possibly Willem Boy, was brought in to finish the eastern half of the south wing. This new architect also planned for a large north wing with towers, connected to the south wing by a long, narrow east wing called "The Long Castle" (Swedish: Långslottet); this new plan would create a U-shaped castle.

And thus, between the two different architects hired by King John III, the new south wing was completed with royal apartments, a hall of state, and church; also included was the rebuilding the southwest tower and construction of a new southeast tower. Two-thirds of the new east wing (The Long Castle) was also completed by the time John III died in 1592. Also during this period, a large garden was laid out at the base of the hill to the east of the castle.