Karl Fritsch (24 February 1864 – 17 January 1934) was an Austrian botanist. He was born in Vienna and educated mainly at the University of Vienna, obtaining his PhD degree in 1886 and his Habilitation in 1890. In 1900 he moved to the University of Graz as professor of Systematic Botany, where he built up the botanical institute. In 1910 he was appointed as director of the university's botanical garden, and in 1916 the new institute acquired its own building. He continued at Graz for the rest of his career, and died there.
Fritsch's extensive research focussed especially on the flora of Austria. He had a particular interest in the family Gesneriaceae and in the taxonomy of the monocots.