The study was performed to investigate the biological activity of Enteromorpha intestinalis. In order to examine its blood anti-coagulant effects, Enteromorpha intestinalis was extracted with cold water, methanol, hot water, HCl and NaOH. In general, the alkali extract of Enteromorpha intestinalis was approximately 17 times stronger than the control. The anti-cancer effects of select extracts(methanol, hot water, 0.1 N NaOH, 1 N NaOH) were determined in human melanoma cells(Bl6/F10), fibrosarcoma cells(HTl080) and breast cancer cells(MCF7) by MTT assay. With the treatment of 250 ${mu}g/m{ell}$ of methanol extracts. HT1080, B16/F10 and MCF7 cell viabilities significantly decreased to 8.06%, 3.62% and 10.10%, respectively. Thus these results strongly support the possibie use of Enteromorpha intestinalis as a functional materials.