Abstract. Eight new species of marine dolichopodid flies from southern Thailand belonging to the genus Thinophilus Wahlberg, 1844 are described and illustrated: Thinophilus boonrotpongi sp. nov.,

The genus Ngirhaphium Evenhuis & Grootaert, 2002 is reported for the first time from Thailand in particular from mangroves on the coast of the Andaman Sea in southern Thailand. Three species were found: N. murphyi Evenhuis & Grootaert, 2002, N. sivasothii Grootaert & Puniamoorthy, 2014 and N. chutamasae sp. nov. The latter species is described and illustrated and a key to all four known species is provided. COI barcode data showed that the new species is most closely related to N. murphyi with a genetic distance of 7%. The distance with the other species is 11 to 12%.

Three new species of Thinophilus Wahlberg, 1844 are described from marine sites on the Andaman Sea coasts in peninsular Thailand: T. inaequalis Samoh & Grootaert sp. nov. belonging to the ‘Thinophilus simplex-group’ sensu Grootaert, 2018, T. plektron Samoh & Grootaert sp. nov., an unplaced species characterised by a long flattened apical spur on the hind tibia, and T. subapicalis Samoh & Grootaert sp. nov. belonging to the ‘Thinophilus spinatus-group’ sensu Grootaert, 2018. New records are given for following species occurring in peninsular Thailand: T. apicatus Grootaert, 2018, T. chaetulosus Grootaert, 2018, T. clavatus Zhu, Yang & Masunaga, 2006, T. evenhuisi Grootaert, 2018, T. lenachanae Grootaert, 2018, T. longicilia Evenhuis & Grootaert, 2002, T. nigrilineatus Grootaert, 2018, T. simplex Grootaert, 2018, T. superbus Grootaert, 2018, and T. yeoi Grootaert, 2018.