Natsuka Masaie (長束 正家, 1562 – November 8, 1600) was a daimyō in the Azuchi-Momoyama period.

[3] Later, because the domain of the Niwa clan was badly reduced after Hashiba Hideyoshi (Toyotomi Hideyoshi) ended the Sengoku period by reunifying Japan, Masaie served him and was given the rule of Minakuchi, Ōmi Province.

Hideyoshi congratulated Masaie on arithmetical faculty and appointed him as one of the Go-Bugyō, along with Ishida Mitsunari, Maeda Gen'i, Asano Nagamasa and Mashita Nagamori.

After Hideyoshi died, in 1600 Masaie and Ishida Mitsunari who was also one of the Go-Bugyō, put up Mōri Terumoto and raised their army against Tokugawa Ieyasu.

At the battle of Sekigahara, Masaie lined their army on Nangu-san with Mōri Hidemoto and Kikkawa Hiroie.