Baron Matsui Keishirō (松井 慶四郎, 28 March 1868 – 4 June 1946) was a Japanese statesman and diplomat.

Matsui was a native of Osaka Prefecture, and a graduate of the Law School of Tokyo Imperial University in 1889.

During the First World War, served as Japanese Ambassador to France and was a plenipotentiary at the 1919 Paris Peace Conference.

[1][2] On the successful completion of this mission, he was awarded with the title of baron (danshaku) under the kazoku peerage system.

He served as Japanese Minister of Foreign Affairs from 7 January to 11 June 1924, under the administration of Kiyoura Keigo and was also appointed a member of the House of Peers in the Diet of Japan.