Abstract: The environmental stress cracking tests of ABS and HIPS were performed by a flexural loading method using rust preventive oil as a solvent, and the effects of stress, solvent and their combination on the tensile and flexural properties of ABS and HIPS were investigated. The results indicated that the tensile and flexural strength of HIPS decreased remarkably due to the combination of stress and solvent, whereas there was almost no influence on the tensile and flexural strength of ABS. In addition, the elongation at break of ABS and HIPS was reduced significantly as a result of the environmental stress, leading to a transition in fracture behavior from ductile fracture into the brittle one.