A new species of Baetidae, Alainites siamensis sp. nov. , is described from Thailand. This closely related to lingulatus Tong & Dudgeon, 2000, laetificus (Kang Yang, 1994) and yixiani (Gui Lu, 1999). Species delimitation based on morphological molecular (mitochondrial COI sequences) evidence provided. The discovery this confirms the wide distribution Waltz McCafferty, 1994 in Southeast Asia.
