The effects of Gracilaria verrucosa (Huds.) Papenf. remediated eutrophication in fish cage-farming areas were studied.at Xiangshan Harbor, Zhejiang Province in May 2007. The resuIts demonstrated that the effects of bioremediation of eutrophication of mariculture waters by G. verrucosa were obvious. The specific growth rate of G. verrucosa with single cultivation was higher than co-culture of G. verrucosa and fish, it could reach to as high sa 9.9% in 12 days. NH4-N removing efficiency of G. verrucosa could reach to as high as 86% in 10 days. DO in bioremediation area was significantly higher than that in non-bioremediation area (p<0.05), COD, NH4-N, NO3-N, NO2-N, PO4-P in bioremediation area were significantly lower than that in non-bioremediation area (p<0.05). The N, P concentration exceeded the 4th class of seawater specified before bioremediation, after 10 days the N, P concentration were greater than the 4th class of seawater specified by cultivation of G. verrucosa. The effect of G. verrucosa remediated eutrophication with co-cultivation was better than single cultivation of G. verrucosa. Large-scale cultivation of G. verrucosa could be a good solution to the problem of eutrophication due to their capability of removing nutrients.