Sassa Narimasa (佐々 成政, February 6, 1536 – July 7, 1588) was a Japanese samurai lord of the Sengoku through Azuchi–Momoyama periods.

In 1570, Narimasa participated in the Siege of Kanegasaki, leading a few armed forces of horse guards, and worked to support Hashiba Hideyoshi using a firearms troop.

In 1580, he was involved in stabilizing the Etchu Province, against an uprising of Ikko sect followers who supported Jimbo Nagazumi.

In 1582, after Oda Nobunaga's death at Honnō-ji, at the Kiyosu meeting, Narimasa took the side of Shibata, but he could not participate in the battle of Shizugatake in 1583, since he could not leave Etchu where he was preparing for the attack of the Uesugi army at Matsukura Castle (Toyama Prefecture).

In 1584, during the battle of Komaki Nagakute, he and the Tokugawa alliance unsuccessfully challenged the Toyotomi force under Maeda Toshiie at the Siege of Suemori.

[5] In 1588, however, due to difficulties in suppressing a Higo Province local revolt, he committed suicide (seppuku) by Hideyoshi's instruction.