Abstract: A taxonomic revision of the genus Lasianthus Jack. from Thailand is made based on specimens in BKF, BK, L, AAU, K, BM, E, P, KEP, SING and PSU etc. Three species and three varieties are described as new; a new combination, L. trichophlebus subsp. barbellatus ( Ridley) H. Zhu, is made; eight species and five varieties are found to represent new records to Thailand; seven species, i.e. L. brevidens Craib, L. densifolius Miq., L. incomptus Craib, L. scalaris Craib, L. penicillatus Craib, L. virgatus Craib and L. zambalensis Elmer, axe reduced to synonyms; two species, L. brevipes Craib and L. lowianus King et Gamble are moved to the genus Saprosma; the delimitation of some species is clarified. As a result, fifty-two species, one sub-species and twelve varieties are recognized in the genus Lasianthus from Thailand.

Key words: Lasianthus Jack., Rubiaceae, Taxonomic revision, Thailand