Nagao Ariga also spelled Nagao Aruga (有賀 長雄, 13 November 1860 – 17 June 1921) was a Japanese legal expert during the Meiji period.

In addition to law, he also studied sociology at Tokyo Imperial University.

[1] During the Sino-Japanese war, he advised Field-Marshall Ōyama Iwao on issues of international law.

[2] In 1913 he accepted the invitation by Yuan Shikai, to prepare a draft constitution for the new Chinese republic, together with Ushikichi Nakae [ja] (中江 丑吉).

Ariga doubted that China was ready to implement a liberal democracy and recommended a balance between monarchy and republic.