Polyclonal antibodies against three red tide algae with different size, Heterosigma akashiwo, Gymnodinium sp and Alexandrium catenella were raised in this study. Block affinity treatment was done to enhance the specificity of the antibodies. The titer of three polyclonal antibodies was determined by indirect enzyme-linked immunosorbent assay, and the specificity against polyclonal antibody was determined by indirect competitive enzyme-linked immunosorbent assy(icELISA). The result showed that Heterosigma akashiwo and Gymnodinium sp antibodies without block treatment got titer higher than 1:32000 and 1:10000, respectively, an indicating of high affinity antibodies. The titer of Alexandrium catenella antibody reached 1:2500, relatively lower than the previous two. The specificity of three polyclonal antibodies after affinity treatment was raised remarkably. However, the titer declined. All the polyclonal antibodies showed a high affinity with their own cells. Polyclonal antibodies were not remarkable cross reacted with other algae in the icELISA, The antibody of Alexandrium catenella reacted to its own cells, no cross activity was found with Alexandrium tamarense, which will be applicable in distinguishing species within the genus. The immunology technique was specific, sensitive and simple with low expend. This was provide a valuable tool for further experiment and had signafication to qualitative and quantitative monitoring of red tide algae.