The study was conducted to determine the distinguishing characteristics of the fourth-instar larvae that used to identify the six species of mosquitoes (Diptera: Culicidae) in Basrah Province. Some morphological characteristics, pectin teeth, comb scales, lateral palatine brush filaments, and microspine patterns on the siphon were studied by using the scanning electron microscopy technique. The results showed that there are morphological differences in these micro-structures between the species, Aedes caspius (Pallas, 1771), Culex pipines (Linnaeus, 1758), Culex pusillus Macquart, 1850, Culex tritaeniorhynchus  Giles,1901, Culiseta longiareolata (Mecquart, 1838) and Uranotaenia unguiculata Edwards, 1913.