The larva of Amphigomphus somnuki Hämäläinen, 1996 is described for the first time based on an emerged male specimen from Chiang Mai Province, and several F-0 larvae collected in other provinces of Thailand. The larva of A. somnuki is the smallest and differs from A. nakamurai Karube, 2001 by the caudal appendages densely covered with minute spiniform setae, and from A. hansoni Chao, 1954 by the male epiproct with the dorsal tubercles at 0.65 the length of the epiproct. New province records for A. somnuki and the first records of Stylogomphus Fraser, 1922 for Thailand are provided.
Keywords: Odonata, Anisoptera, dragonfly, description, new records, Thailand.