Toivo Ilmari Hannikainen (19 October 1892 in Jyväskylä – 25 July 1955 in Kuhmoinen) was a Finnish composer.
Hannikainen was the son of Pekka Juhani Hannikainen and the brother of , both of whom were composers and of Tauno Hannikainen who was a conductor. After studying at the University of Helsinki (1911–14), he became a pupil of Franz Schreker at the Musikakademie in Vienna, and continued his studies with Alexander Siloti in Saint Petersburg (1915–17) and with Alfred Cortot in Paris (1919). Returning to Finland, he taught piano at the Helsinki Conservatory and later gained a Professorship at the Sibelius Academy.
Hannikainen steered Finnish classical music from late Romanticism towards Impressionism. In addition to his piano miniatures, which best illustrated this development, he composed one opera, one piano concerto, one piano quartet, lieder, and film scores (notably, Sången om den eldröda blomman, Sweden, 1934).