The result of effect of temperature and irradiance on photosynthetic and respiratory responses of Gracilariopsis chorda and Gracilaria parvispora indicated that temperature and irradiance affected directly physical activities of the two investigated species, especially photosynthesis and respiration. Gp. chorda and G. parvispora could survive at temperature from 8 to 38°C and irradiance from 0 to 500 umol photons m2/s. Although signals of photo inhibition were found in both species at 32 and 36°C, t photo:inhibition was not observed at all of investigated irradiance levels. Q10 values reached from 1 to 3 in temperature range from 16 to 20, 20 to 24 and from 24 to 28°C in both species. As a result, optimum temperature for photosynthesis and respiration in both species was from 20 to 28°C.