Abstract: Extracellular products（ECP）of Aeromonas hydrophila (Ah) GYK1, isolated from mandarinfish, Siniperca chuatsi and other 7 strains of Ah and 1 strain of A.sobria were extracted by cellophane cover technique. Some characteristics of the ECP of GYK1 strain were analyzed. The ECP of GYK1 strain had enzyme activity of caseinase, amylase, lipase and gelatinase, but had not activity of urease. The ECP also had strong hemolytic activity. The hemolytic titer of crude ECP, with protein concentration of 365 gmL-1, to erythrocyte of mandarinfish was 213, to that of other two kinds of fishes and five kinds of mammals were between 211～214. The result of SDS-PAGE showed that the band with molecular weight about 35 kDa is the common protein band of the ECP of the tested 8 Ah strains. ECP of GYK1 strain was purified and the band of 35 kDa was obtained by HiprepSephacryl S-200 high resolution chromatography. And the purified product had hemolytic activity, but was weaker than that of the crude ECP. The hemolytic titer of crude ECP to mandarinfish and mouse was 213 and 212, while that of the purified ECP was both 25.