Karel Ondricek (1865–1943) was a Czech violinist. He was the brother of František and Emanuel Ondricek. He first studied with his father, Jan Ondricek, then with Antonín Bennewitz at the Prague Conservatory, which he did not complete. For a time, he played in his father’s orchestra.
Ondricek became first violinist in the orchestra of the National Theatre in Prague. He took part in premieres of chamber works by Antonín Dvořák: the Four Romantic Pieces, Op. 75 (1887), with Dvořák at the piano; the String Trio, Op. 74 (1887); the Piano Quintet, Op. 81 (1888); and String Quartet No. 1, Op. 2, written in 1865 but apparently not performed in concert before 1888. Ondricek taught Jan Kubelík.
From 1899 to 1902, he played in the Boston Symphony Orchestra and the Kneisel Quartet. Around 1910, he led his own musical trio.