Salinity tolerance is an important trait that governs the ecology of disease‐vector mosquitoes by determining their choice of larval habitat, and consequently their ecological and geographical distribution. Here, we used laboratory strains to determine the osmotic responses of larvae of obligate freshwater disease‐vector mosquitoes (Aedes aegypti, Aedes albopictus, Anopheles coluzzii, An. gambiae, Culex pipiens, and Cx. quinquefasciatus) and assessed their relationship with salinity tolerance. First, we analyzed the acute dose–mortality response of fourth‐instar larvae to salinity; then, we measured their hemolymph osmolality after 24‐h exposure to varying salinities. We found that Ae. albopictus was the most tolerant species, followed by An. coluzzii, Ae. aegypti, Cx. quinquefasciatus, and An. gambiae, in decreasing order. Cx. pipiens was the least tolerant species. All mosquitoes were hyper‐iso‐osmoregulators, but with species‐specific differences. Specifically, hemolymph osmolality in deionized water varied among species, and Cx. pipiens and the two Aedes species showed the lowest and highest osmolality. Although all species were osmoconformers at higher salinity values, hemolymph osmolality approached environmental osmolality more rapidly in species of the Culex genus, compared with Aedes species where it increased slowly. Moreover, hemolymph osmolality in deionized water was significantly correlated with tolerance to salinity across species. This could allow predicting the salinity tolerance of untested species on the basis of their osmoregulatory ability. However, this correlation disappeared when considering the hemolymph osmolality of larvae exposed to salinities higher than deionized water.