Abstract: The purpose of this study was to investigate the effects of six mine floatation reagents on algae. The acute toxicities are in the order No.2OilFu0145YxMPAS-808.The 96-h EC50 for Scenedesmus obliquus of the above six reagents are 41.2, 50.1, 82, 177.8, 198.2 and 900 mg/1 respectively. No.2 Oil had the highest toxicity, while S-808 had the lowest toxicity. Some deformed cells were found in cultures exposed to 0145 for 48 hr, but in the cultures exposed to the other five reagents, no deformed cells were observed at concentrations higher than EC50. The toxicities of No.2 Oil, 0145 and MPA decreased markedly after they had been kept at ambient temperature for 10 days. Chronic tests indicate that the algae can remove S-808. The algae exposed to 100 ppm S-808 caused a 48％ reducation in the optical density of the S-808 solution. The reagent 0145 can inhibit algal photosynthesis. The photosynthetic rate of algae exposed to 50, 100 and 200 ppm 0145 for 4 hr decreased by 15, 34 and 36％ respectively.