Effects of temperature and salinity on photosynthesis and productivity of G. tenu-istipitata have been studied. All the experimental materials were controlled under lightintensity of 9000 Lux and with defferent temperature (25--35℃) and salinity (0-45‰). The experimental data indicated that peak net photosynthesis was 13.83μl O₂/mg dry weight per hr and maximum productivity was 5.07g C/m² per day at 25℃,26‰. According to Kanwisher's calculation method, G. tenuistipitata could ideallydouble their own mass in 5 days at 20℃ or 30℃. The optimum salinity for photosyn-thesis ranged at 19--26‰ or 26--32‰, respectively. Photosynthesis saturation wasgenerally about 20 times of respiration and varied with the ecological factors.Different parts of thallus bad different photosynthetic rate. The terminal part ofthallus doubles to that of the base, and differnet part of the thallus also had evidentlydifferent respiratory rate. It is due to uneqilibrium of metabolic activity in differentparts of the thallus. Therefore, growth rate of the terminal part was much faster thanthat of the basic and middle parts.During the period from October 1981 through June 1982, the response of G. tenu- istipitata to temperature and salinity has been measured inshore at the Shantou Har-bour. From November to next April, temperature ranged 15--22℃ and salinity 14-18‰. At that time, the plant grew most luxuriantly. Optimum growth rate of the G.tenuistipitata was 0.27cm/day and the production of biomass was 75g/m²(dry weight)at the Shantou Harbour. In May, sometime when water temperature reached 27--30℃,the plant could grow normally. It reveals that G. tenuistipitata could better adapt tohigh temperature.