This study was conducted to elucidate the effects of pH on the toxicity of cadmium, cobalt and copper to the green alga Scenedesmus bijuga. The sublethal concentrations of Cd²⁺, Co²⁺ and Cu²⁺ were obtained at 10^-6, 10^-5, 10^-5 M, respectively. A standard initial inoculum of the tested alga was used to inoculate the culture flasks containing Kuhl's medium with different pH values (4, 6, 8, 10 and 12) supplied with the sublethal concentrations of each tested metal.  The results revealed that the growth of Scenedesmus bijuga increased with increasing pH. However, the accumulation, the accumulation factor and the amount of free ionic forms of each metal decreased.  Generally, it appears that the tested metals exert more toxic effect in acidic than in alkaline pH conditions.