Johan Arndt (Jukka) Lehtosaari (15 January 1889 – 2 September 1939; original surname Forsman) was a Finnish politician, born in Kärkölä.
He joined the Communist Party of Finland (SKP), founded in Moscow by political exiles on 29 August 1918.
He returned clandestinely to Finland in 1919, but was arrested by Finnish authorities and was given a prison sentence for sedition.
He recovered his liberty in 1926 and moved to the Soviet Union, where he found work as a teacher at the Communist University of the National Minorities of the West and at the International Lenin School.
However, in January 1938, during the Great Purge, he was arrested as suspected of counterrevolutionary activities.