Orange-spotted Grouper (Epinephelus coioides) which inhabits subtropical and tropical areas, has become a very popular species of marine teleost currently being cultured in China. Metabolic rate is the most fundamental biological rate as it represents the rate of energy uptake, transformation and allocation. Oxygen consumption is a widely studied indicator of metabolic rate, and measurement of oxygen consumption rate is often used to examine energy utilization and stress in aquatic animals. The aim of the present study is to investigate the effects of temperature (21℃, 24℃, 27℃, 30℃ and 33℃), pH (6.5, 7.0, 7.5, 8.0 and 8.5) and body wet weight (mean values:15.64 g, 35.80 g, 65.67 g and 95.93 g) on oxygen consumption rate (MO2), ammonia excretion rate (MTAN) of Orange-spotted Grouper juveniles cultured in low-salt water (salinity 12) by the intermittent flow respirometry system with ecological methods in laboratory. Data were analyzed by using the one-way ANOVA, followed by Ducan test. All analyses were performed with a significance level of P < 0.05. The results showed that temperature strongly affected both MO2 and MTAN. The MO2 and MTAN increased significantly (P < 0.05) with an increase in temperature from 21℃ to 33℃ (Table 1). The linear equation between the MO2, MTAN and temperature (T) were established (MO2 = 6.0826T﹣8.9704, R2 = 0.9127; MTAN = 0.2248T﹣0.7731, R2 = 0.7792) (Fig. 2). Over the entire experimental temperature range (21﹣33℃), the respiration temperature coefficient Q10 and excretion temperature coefficient Q10 were 1.51, 1.54, respectively, and the lowest values were found between 27 and 30℃. The optimal temperature for the juvenile lied between 27 and 30℃ (Table 2). Both MO2 and MTAN were significantly affected by pH (P < 0.05) (Table 1), being increased first then decreased with pH increase. The relationship between MO2, MTAN and pH was modeled by a quadratic equation (MO2 = ﹣15.241ApH2 + 234.98ApH ﹣737.42, R2 = 0.7888; MTAN =﹣1.1477ApH2 + 18.073ApH﹣65.369, R2 = 0.7557) (Fig. 2). Both MO2 and MTAN decreased significantly with increased body wet weight (P < 0.05) (Table 1), and their relationship with body wet weight (W) could be represented by power equations (MO2 = 310.61W ﹣0.1972, R2 = 0.8653; MTAN = 9.9167W ﹣0.2043, R2 = 0.8257). The oxygen consumption (RO2) and ammonia excretion (RTAN) increased with increase in body mass, and their relationship with body wet weight was modeled by power equations (RO2 = 0.3106W 0.8028, R2 = 0.9907; RTAN = 0.0099W 0.7957, R2 = 0.9863). The averages of oxygen-nitrogen ratio (O︰N) at different temperatures, pH values and body wet weights were 25.90, 28.65 and 28.19, respectively (Table 1), which indicated that Orange-spotted Grouper juvenile cultured in low- salt water utilized protein-lipid dominated metabolism.