Natsuka Masaie (長束 正家; 1562 – November 8, 1600) is a daimyo in Azuchi-Momoyama period and five bugyo appointed by Toyotomi Hideyoshi.

Born in Owari Province, Masaie served Niwa Nagahide who was a retainer of Oda clan. Because the domain of Niwa clan was badly reduced after Hashiba Hideyoshi (Toyotomi Hideyoshi) ended Sengoku period by reunifying Japan, Masaie served him and was let rule Minakuchi ,Omi Province. Hideyoshi congratulated Masaie on arithmetical faculty and appointed him as one of five bugyo. After Hideyoshi died, in 1600, Masaie and Ishida Mitsunari who was one of five bugyo put up Mori Terumoto and raised their army to Tokugawa Ieyasu. At the battle of Sekigahara, Masaie lined their army on Nangu-san with Mori Hidemoto and Kikkawa Hiroie. However, Masaie was prevented from fighting by Hiroie and finally routed to Minakuchi. Setting fire to Minakuchi Castle, he committed suicide.

His grave is at Anraku-ji, Shiga Prefecture.