This study examined the effects of reactive black 5 (RB5) on peroxidase, lipid peroxidation and total chlorophyll content of Phaseolus vulgaris L. cv. "Gina". The beans were exposed to 200, 260, 338, 439, 571, 743, 965 and 1255 m/L of RB5. Significant increase in peroxidase activity was identified in RB5-treated plants. The effects of RB5 on lipid peroxidation were analyzed. MDA content of RB5-treated plants was found to be higher in all application groups, except that of 439 mg/L. In addition, it was found that total chlorophyll content increased in all applications when compared to control group. Our findings indicate that RB5 causes significant changes in peroxidase activity, MDA content, and pigment system.