Fritz Sarasin, full name Karl Friedrich Sarasin (3 December 1859 – 23 March 1942) was a Swiss naturalist.
He was a second cousin of Paul Sarasin. They made a scientific expedition to Celebes (now Sulawesi).
Fritz and Paul Sarasin are commemorated in the scientific names of five species of reptiles: Amphiesma sarasinorum, Nessia sarasinorum, Pseudorabdion sarasinorum, Rhacodactylus sarasinorum, and Sphenomorphus sarasinorum.
He has published some of scientific works together with Paul Sarasin.