| Ōuchi Sadatsuna | |
| Native Name: | 大内 定綱 |
| Birth Date: | 1545 |
| Death Date: | 1610 |
| Birth Place: | Mutsu Province |
| Commands: | Obama Castle, Hobara Castle, Maezawa Castle |
| Battles: | Battle of Suriagehara, Korean Campaign |
was a Japanese samurai and military commander of the Sengoku period. He was the lord of the Obama Castle.[1] [2] Sadatsuna belonged under the command of Tamura Kiyoaki. But Sadatsuna switched from the Tamura clan to the Ashina clan and he became independent of the Tamura clan.[3] Later, he served the Date clan and became a senior retainer.[4] [5]