Kaarlo Castrén (28 February 1860 – 19 November 1938) was a Finnish politician and Prime Minister of Finland.

Castrén was born in Turtola and graduated in 1887 as a Bachelor of Law.

From 1888 to 1892, he worked in the finance division of the Senate of Finland, and from 1888 to 1898 in the Castrén & Snellman attorneys-at-law office.

In November 1918, Castrén was named Minister of Finance.

[2] He served as Prime Minister of Finland from 17 April to 15 August 1919.