Abstract: In this study, Tribonema bloom taken from the bottom of pond were exposed to different concentrations of sulfuric copper and isothiazolone-ketone, and sampled at different time. Then the chlorophyll a (Chl a) contents were measured by spectrophotometer, and malondialdehyde (MDA) content, superoxide dismutase (SOD) and catalase (CAT) activities were measured by using corresponding kits. The results showed that the effect concentration 50%(EC50) of copper sulfate and isothiazolone-ketone on the Tribonema blomm for 24 h, 48 h, 72 h, 96 h were 5.551, 4.543, 3.646, 2.898 mg/L and 13.712 mg/L, 9.858, 8.680, 5.114 mg/L, respectively, and the toxicity enhanced with the concentration increasing. At the concentration of 2.40 mg/L, the Chl a content, SOD, and CAT activities reached to the minimum, but the MDA content achieved to the peak, suggesting that the cells of Tribonema sp. completely disintegrated at this time. At the concentration of 0.42 mg/L, no significant differences between measurements and control group were observed, indicating that low concentrations of copper presented less toxicity within 96 h. The results indicate that the two algaecides both can suppress or kill Tribonema bloom and copper sulfate had more toxic to algaecide compared with isothiazolin-ketone.