Coral bleaching occurs when cell density and/or the concentration of photosynthetic pigments of the endosymbionts; zooxanthellae are decreased. It has been proposed that the cause of this may be due to environmental stresses such as elevated temperature and decreased in water salinity. This study analysed characteristics of the endosymbiont; Pocillopora damicomis to clarify the potential importance of temperature and salinity on zooxanthellae. The growth responses of axenic culture were observed at 3 levels of temperatures; 25 (control), 27 and 33. At each temperature level, 5 levels of salinities; 10, 15, 25, 28 ZcontrolX and 33 psu were assigned. Sampling cells were enumerated every 2 days for 14 days from which the specific growth rates were determined. The decreasing specific growth rate of zooxanthellae were observed at high temperatures and low salinity levels. At the highest temperature, 33 C at all levels of salinity, a decrease in growth rate of zooxanthellae was found. While at 25 and 27 C, a decrease in growth of zooxanthellae was observed only at the lowest salinities; 10 and 15 psu. These results suggest that both temperature and salinity may have a singular and combined affect on the growth rate of zooxanthallae.