Pekka Juhani (P. J.) Hannikainen (December 9, 1854, Nurmes, Finland – September 13, 1924, Helsinki) was a Finnish composer and the head of a famous Finnish musical family.
Hannikainen was born in Nurmes but moved to Jyväskylä to attend school. He then studied chemistry in Helsinki and later lived in Jyväskylä and Helsinki.
Hannikainen was the founder and conductor of the first Finnish student choir, the Ylioppilaskunnan Laulajat, from 1882 to 1885. He also founded the Mieskuoro Sirkat choir in 1899. From 1887 to 1891, he was the editor of the first Finnish music magazine, Säveleitä.
He was the father of the pianist Ilmari Hannikainen (b. 1892), the composer Väinö Hannikainen, and the cellist Tauno Hannikainen (b. 1896). He is buried in the Hietaniemi Cemetery in Helsinki.