Niki Sadanaga served as a bushō during the late Muromachi and early Sengoku periods.  Sadanaga was a member of the Ise-Niki clan.  He served as the military governor of Ise Province.  His common name was Jirōshirō and childhood name was Chiyokiku.  His father was also a bushō.

From 1481 to 1483, Sadanaga was involved in debt claims with 建誉蔵主

In 1483, Sadanaga was ordered to vacate and turn-over the territory of the Rokuō Temple in Tango Province.

From 1484 to 1485, he instigated riots in regard to Kanbayashi 吉忠番 in the territory of the Shōkoku Temple in Tanba Province.

In 1487, Sadanaga was killed in battle against the Yumiba clan in the Ōmi Expedition led by Ashikaga Yoshihisa, the ninth shōgun of the Muromachi bakufu.  Along with Sadanaga, twelve servants and ten rank-and-file soldiers were killed.  Prior to this battle, it was rumored that the Yasutomi and Uehara clans who served the Hosokawa-Keichō family allied with Rokkaku Takayori.