Reproductive effort and spawning frequency of the two palaemonid prawns, Exopalaemon modestus and Palaemon gravieri, were investigated. In both embryos of the two species, egg size was larger in E. modestus than in P. gravien but for a given size, number of eggs (EN) was fewer in E. modestus. The statistical results revealed that there were significant differences in egg size and EN between the two species. E. modestus living in freshwater environments had larger and fewer offspring than P. gravieri inhabiting marine environments. These findings are consistent with predictions from r- and K-selections models. Reproductive effort (RE) also was higher in E. modestus, suggesting the possibility for E. modestus to invest larger amount of energy per individual offspring. In the two prawns the ovarian dry weight of females with eyed eggs was significantly higher than those with non-eyed eggs. This indicates that the ovarian maturation occurs during the period between the two embryonic stages, suggesting females being potentially of continuous breeding within a single reproductive period. In the both species brood loss did not occur during the incubation period.