Gynacantha chaplini sp. nov. is described based on a male collected from the north-eastern region of Bangladesh. Distinguishing features of the adult male are illustrated and discussed. Gynacantha chaplini sp. nov. is distinguished from its congeners by a dark brown trapezium-shaped mark on the postfrons. An updated key is provided to identify the males of the Gynacantha species known from South Asia (Bangladesh, Bhutan, India, Nepal, Pakistan, Sri Lanka).