This work examines the effects of five pesticides on Chlorella vulgaris. For this purpose, C. vulgaris cultures were exposed to 5 pesticides (azinphos-methyl, malathion, parathion, terbufos, trichlorfon) of different concentrations for 96 hour. After exposure, EC50 values, culture growth, chlorophyll_a, dry weight and pesticide accumulation analysis were performed. The results indicated that average toxicity of the five pesticides were as malathion > parathion > terbufos > azinphos-methyl > trichlorfon order. However, the statistical analysis revealed that the degree of effects of the effective pesticides on Chlorella vulgaris was determined to be ranked as azinphos-methyl > trichlorfon > terbufos > parathion-ethyl > malathion. The result obtain in GC/MS show that all pesticides were accumulated in C. vulgaris in high amounts. However, the current results need further data to conclude whether this accumulation is due to an absorbtion by an algae cell itself to an accumulation on cell surface. Terbufos was found to accumulate in high amounts in the C. vulgaris. There was a strong variance between toxicity and ecological risk.