Hosokawa Ujitsuna (細川 氏綱, 1514 – January 4, 1564) was a Japanese military commander and Deputy Shogun of the Hosokawa clan in the end of the Muromachi period and Sengoku period of the 16th century. He was the foster son of Hosokawa Takakuni.
In 1543, Ujitsuna raised his armies in revenge for Takakuni who was killed by Hosokawa Harumoto. He was at a great disadvantage at first, because Harumoto had great powers. However, Miyoshi Nagayoshi who was the retainer of Harumoto betrayed Harumoto and took sides with Ujitsuna. In 1549, at last, Ujitsuna pulled off expelling Harumoto to Ōmi Province.
In 1552, Ujitsuna marched his armies along with Nagayoshi, and appointed to Kanrei. However, a puppet of Nagayoshi, Ujitsuna didn't have any powers. After that, Ujitsuna was given Yodo castle at Settsu province and monitored by Nagayoshi.
In 1564, he died in despair and hopelessness.