The present study investigated the critical thermal maxima (CTmax) of red-spotted grouper, Epinephelus akaara under different acclimation temperatures (Tacc). Fish were acclimated at 24°C, 28°C, and 32°C water temperature for 2 weeks. Water temperature was increased at a rate of 1°C/h and CTmax level was measured following the critical thermal methodology (Paladino et al., 1980). The results showed that CTmax values of E. akaara were 35.61°C, 36.83°C, and 37.65°C for fish acclimated at 24°C, 28°C, and 32°C, respectively. The acclimation response ratio (ARR) was 0.26. The CTmax values were significantly correlated with body size. Collectively, it is said that the CTmax value of red-spotted grouper can be affected by different adaptation temperature (24°C, 28°C, and 32°C) and the fish acclimated to a higher temperature has a higher CTmax level. Besides, the CTmax value of 35.61°C−37.65°C indicating the upper thermal tolerance limit for E. akaara under different Tacc (24°C, 28°C, and 32°C). Understanding the thermal tolerance of E. akaara is of ecological importance in the conservation of this species.