Hōjō Ujitsuna (北条 氏綱, 1487 – August 10, 1541) was the son of Hōjō Sōun, founder of the Go-Hōjō clan. He continued his father's quest to gain control of the Kantō (the central area, today dominated by Tokyo, of Japan's main island).
In 1524, Ujitsuna took Edo Castle, which was controlled by Uesugi Tomooki, thus beginning a long-running rivalry between the Hōjō and Uesugi families. Two years later, the Uesugi attacked and burned Kamakura, which was a major loss to the Hōjō symbolically, because the earlier Hōjō clan from which they took their name fell in the siege of Kamakura in 1333.
The Uesugi attacked again in 1535, when Ujitsuna was away fighting the Takeda; however, Ujitsuna returned and defeated Uesugi Tomooki, reclaiming his lands. When Uesugi Tomooki died two years later, Ujitsuna took the opportunity to seize Kawagoe Castle, and secure his control of the Kantō.
In 1526, Hojo Ujitsuna was defeated by Takeda Nobutora in the Battle of Nashinokidaira.
Ujitsuna then went on to win the battle of Kōnodai in 1538, securing Shimōsa Province for the Hōjō.
In 1539 he defeated the Koga Kubo Yoshiaki and gained control of Awa.
Over the next several years before his death in 1541, Ujitsuna oversaw the rebuilding of Kamakura, making it a symbol of the growing power of the Hōjō, along with Odawara and Edo. He was succeeded as head of the Hōjō clan and lord of Odawara by his son Hōjō Ujiyasu.