Leptomonas is a genus of parasitic flagellate protist belonging to family Trypanosomatidae and subfamily Leishmaniinae sensu Maslov & Lukeš 2012.

[1] It is a monoxenous parasite of mainly Hemiptera, Diptera, and Siphonaptera insects.

[2] In addition to Leptomonas, one-host trypanosomatids from insects have been traditionally placed in genera Crithidia, Blastocrithidia, Herpetomonas, Rhynchoidomonas, and Wallaceina.

[3][4] The etymology of the genus name Leptomonas derives from the two Ancient Greek words λεπτός (leptós), meaning "fine-grained, tiny", and μονάς (monás), meaning "alone, isolated" (as an adjective), or "a unit" (as a name).

[5][6] There are 18 species of Leptomonas.