Abstract: Effects of temperature (15,25 and 30℃),light intensity (20,60 and 100 mol/m2/s),nitrogen and phosphorus ratio (1:1; 1:16; 1:128) on hemolytic toxin production of six species of ichthyotoxic algae were studied under laboratory conditions.The results showed that the hemolytic activities of the ichthyotoxic algae in different growth phases were significantly different (p0.05). Chattonella marina,C.ovata,Karenia mikimotoi and Heterosigma akakshiwo exhibited a higher hemolytic activity in exponential phase and a lower hemolytic activity in decline phase.However,Phaeocystis globosa and Prymnesium parvum reached the highest hemolytic activity in stationary phase,and the lowest hemolytic activity of the two algae was detected in exponential phase.The physical environmental factors and nutrition conditions of algae culture also had great effects on the hemolytic activity.The hemolytic activity of single algal cell changed obviously under different conditions of light intensity,temperature,nitrogen and phosphorus limitation.The hemolytic activities of the six algae were positively correlated with light intensities.Except for P.globosa,the hemolytic activities of the other five ichthyotoxic algae showed an increasing trend in temperature range of 15~30℃.Nitrogen and phosphorus limitation promoted the product of hemolytic toxins.