The effect of chronic (2 weeks) temperature (19, 22, 25, 28 and 31°C) on certain non-specific immune parameters of two species of scallops, Argopecten irradians (Lamarck 1819) and Chlamys farreri (Jones & Preston 1904) were studied. The survival ratio of the two species of scallops at 31°C was the lowest. Haemocyte concentration of C. farreri in the 19 and 22°C treatment groups was significantly lower than that of the 25 and 28°C treatment groups but significantly higher than that of the 31°C treatment group. With elevation of seawater temperature, the alkaline phosphatase (ALP) and acid phosphatase (ACP) activities in sera of two scallop species increased and reached the peak at 25°C and then decreased. However, the specific activity of ALP and ACP of the 31°C treatment group was the highest. The results demonstrated that temperature of seawater significantly affected immunity of scallops. The concept that the stress of high environmental temperature on C. farreri may be partially responsible for the mass mortality of the organism is also introduced.