Matsuzo Nagai (永井 松三, Nagai Matsuzō, March 5, 1877 – April 19, 1957) was a Japanese diplomat and Olympic Games activist.

In 1930, he formed part of the Japanese delegation to the London Naval Conference.

In 1936, he served as Minister of Transportation, and was an active supporter of naval expansion plans.

In 1937, he was active in the Japanese governmental committee which was charged with preparing the Olympic games scheduled to take place in Tokyo in 1940, which was eventually cancelled.

[4] He received the Grand Cross of the Royal Swedish Order of the Polar Star in 1928.