We investigated the optimum salinity and temperature conditions for the mass culture of small rotifer, Keratella sp.. In the salinity experiment ranging from 0-34‰, the population growth of Keratella sp. drastically increased continuously up to 15‰, and then slightly increased over 20‰. Their maximum density reached 1,007 inds./mL at 0‰. A pre-reproductive phase was shorter in low salinity than in high salinity. The highest number of offspring per female (10.2 inds.) and lifespan of the female (10.7 days) were obtained at 0‰, but there were no significant differences compared to those at 5‰. In the temperature experiments ranging from 16-$32^{circ}C$, the highest maximum density (1,766 inds./mL) was shown at $24^{circ}C$. The number of offspring per female significantly increased with increasing temperature, and the highest number of offspring per female was 10.4 inds. at $24^{circ}C$. The lifespan of female increased with decreasing temperature and the longest lifespan was 12.8 days at $16^{circ}C$.