Matsui Keishirō (, 28 March 1868 - 4 June 1946) was a Japanese diplomat during the Showa period and later Minister of Foreign Affairs. He graduated from the Law School of Tokyo Imperial University in 1889, and entered the Foreign Ministry the same year. In 1890, he was given a post in the Japanese embassy in Seoul in 1890, and in 1895 was sent to the United States. In April 1889, he served in London. In 1902, he was re-assigned to Beijing. He returned to Japan in 1913.