Mosquitoes (Diptera; Culicidae) are considered as one of the most medically important   insect  groups however, scientific studies on this group are limited mainly to the major vector species in the  country.  Hence, the present study was to investigate the diversity and seasonal variation of  mosquito species and their natural enemies in selected habitats of Galle District, Sri Lanka.  Adult and larval mosquito surveys were done in monthly basis, (January 2017 to December  2019) in eight study sites [Urban (US), Rural (RuS), Coastal (CoS), Natural inland (NIS), Coastal inland mixed (CIMS), Rocky (RocS), Mangrove (MS) and Forest (FS)].Hand collection (HC), cattle-baited net collection (CBNC) and cattle-baited hut collection (CBHC) were used for collecting adults. Larval sampling was done using pipetting, siphoning, dipping and netting. The  seven abiotic variables [Temperature, pH, salinity, conductivity, Total Dissolved Solids (TDS),  Turbidity and Dissolved oxygen (DO)] of the water in larval breeding habitats were measured on site. The density of natural enemies of mosquitoes in study sites and their feeding efficacy on vector mosquito larval species was observed. The coexistence of larvivorous mosquito larvae (Lutzia fuscana) on the vector mosquito larvae (Aedes albopictus) was studied. Standard diversity indices (relative abundance, Shannon-weinner diversity, species richness, evenness) Canonical correspondence analysis and the density index were used to analyze the data. The relationship of larval mosquitoes with physiochemical parameters of their breeding sites was analyzed.  Total number of 58298 adult mosquitoes was recorded in 27 species (Anophelese (12), Culex (8), Aedes (3), Mansonia (3) and Armigerus spp) and Cx.gelidus was the predominant by representing 17.95% (n=10318).The highest degree of species evenness recorded in the MS (0.818).The RuS had the highest species diversity (𝐻= 2.393) .The US, RuS and NS showed the highest species richness (𝑆=26).A total of 10365 larval mosquitoes of 21 species (Anophelese (8  spp), Culex (4 spp), Aedes (4 spp), Lutzi spp, Tripteroid spp, Armigerus spp, Mansonia spp and  Toxorhinchites spp) were recorded and Ae.albopictus was the dominant 32.71%  (n=3390).Among the nineteen breeding site types agriculture fields showed the highest species diversity (𝐻= 2.05), species richness (𝑆 = 10) and pet feeding cups had the highest species evenness (0.978). Water salinity was significantly different in natural plants, agricultural fields and rock-pools (P