Objective To investigate the species composition of adult mosquitoes in residential areas of Nong county of Savannakhet province in southern Lao PDR, and to provide a scientific basis for developing prevention and control strategies and measures for local important mosquito-borne diseases. Methods Adult mosquitoes were captured using the light-trap method (overnight) and electric mosquito trap method in residential areas, and all mosquitoes were identified by morphological classification. Results A total of 9 415 mosquitoes belonging to 44 species in 11 genera of 3 subfamilies were captured in residential areas of Nong county of Savannakhet province from August to September, 2018. Armigeres subalbatus and Culex tritaeniorhynchus were dominant species, accounting for 44.43% (4 183/9 415) and 20.73% (1 952/9 415) of total collected adult mosquitoes, respectively; Anopheles minimus, Aedes albopictus, and Ae. aegypti had lower proportions, accounting for 1.96% (184/9 415), 1.09% (103/9 415), and 0.54% (51/9 415) of total collected adult mosquitoes, respectively. Conclusion Mosquito species are abundant in Nong county of Savannakhet province in southern Lao PDR. Culex tritaeniorhynchus (Japanese encephalitis vector), An. minimus (malaria vector), and Ae. albopictus and Ae. aegypti (dengue vectors) are distributed in this region, so it is suggested that the local healthy department should strengthen the monitoring of important mosquito-borne disease vectors mentioned above.