Antialgail activity extractions EPME(methanol extracts of Enteromorpha prolifera)were separated by liquid-liquid extraction and silica gel column chromatography to isolate and identify antialgal activity compounds in EPME.By liquid-liquid extraction,the four kinds of components(Ⅰ,Ⅱ,Ⅲ and Ⅳ)were obtained.Their yield was 29.0%,19.0%,12.7% and 5.45%,respectively,but only component Ⅱ has only obvious inhibiting activity.The inhibitory effect of Karenia mikimitoi,Skeletonema costatum and Alexandrium tamarense by component Ⅱ(1.0 g/L)was 43.4%,44.9% and 54.3% on Day 12,respectively.The five kinds of fractions(Ⅱ-A,Ⅱ-B,Ⅱ-C,Ⅱ-D and Ⅱ-E)were obtained by silica gel column chromatography,respectively.The fraction B(Ⅱ-B)and fraction C(Ⅱ-C)inhibited significantly the growth of all test microalgae,and these two fractions caused cells cavities and pieces.Further,these two fractions(Ⅱ-B andⅡ-C)were analyzed by wavelength scanning,compound identification test and silica gel GF₂₅₄ thin-layer chromatography.This paper identified containing lactone and coumarins in them and determined the appropriate developing agent by silica gel GF₂₅₄ thin-layer chromatography for subsequent separation and purification.This paper provided solid experiment foundation for further study.