Arhopala atosia is a species of butterfly belonging to the lycaenid family described by William Chapman Hewitson in 1869. It is found in Southeast Asia - Borneo, Sumatra, Bangka, Pulau Laut (A. a. atosia), Thailand, Indochina, Peninsular Malaya, Singapore (A. a. malayana Bethune-Baker, 1903), Burma (A. a. aria (Evans, 1932)), Langkawi, Mergui (A. a. jahara Corbet, 1941) and Palawan (A. a. aricia (Staudinger, 1889)).
Above the male is not lilac, but mostly dark blue with a very feeble violet tint, although also more intensely lilac-tinged specimens have been ascertained. Beneath very similar to pseudomuta, but in the female the postdiscal band of the hindwing is more irregular, and the 4th spot of the postmedian band of the forewing still more distally removed. The female has a black distal margin of about 3 mm width.