Mochizuki Keisuke (望月圭介, 1 April 1867 – 1 January 1941) was a statesman, politician and cabinet minister in Taishō and early Shōwa period Japan.

Mochizuki was born on Ōsakikamijima, an island in the Seto Inland Sea, now part of Hiroshima Prefecture, where his father was an entrepreneur and ship owner.

In his early career, Mochizuki spoke out strongly against factionalism in the Diet based on old clan-based affiliations.

He later joined the Kenseitō political party, but was recruited as one of the founding members of the Rikken Seiyūkai by Itō Hirobumi in 1900.

He rose to a high rank within the party, eventually serving as secretary-general during the administration of Prime Minister Hara Kei.