Otto Kotilainen (February 5, 1868 Heinävesi – August 9, 1936 Helsinki) was a Finnish composer. He was from every part of the musical family. He practiced singing from an early age. He attended Kerma Primary School, which was also attended by the poet Alpo Noponen. They were childhood friends. Later, Noponen made lyrics to some of Kotilainen’s compositions.

Kotilainen graduated as a teacher from Jyväskylä in 1890. In 1893 Kotilainen came to Helsinki as a teacher. At the same time, he studied composition at the Helsinki College of Music and later as a student of Jean Sibelius.

His most well-known songs include the Christmas songs Varpunen jouluaamuna (lyrics Sakari Topelius) and Kun joulu on (lyrics Alpo Noponen) as well as many other songs, such as Kyyhkynen kylpee, Laulu oravasta, Pilvitanssi. In addition to these, Kotilainen composed music for horn, violin and piano, numerous choral songs such as Väinölän väki (lyrics Eino Leino) and drama music. He also helped organize the Heinävesi Song and Music Festival.

The resident loved Heinävesi and especially its streams and rapids. He had a summer home in Varisselkä in Varisvesi. He was an avid fisherman. Eino Leino and Juhani Aho, among others, were often guests at his summer residence.