The effect of Cu2+ on the growth of argassum thunbergii argassum thunbergii different growth periods of Syoung sporophyte was investigated. Both early and late Sargassum thunbergii young sporophyte were very sensitive to Cu2+. For early Sargassum thunbergii young sporophyte, Above 5 ug/Lof Cu2+ concentration, growth of young sporophytes were seriously inhibited. when Cu2+ concentration reach or exceed 250ug/L, young sporophytes could hardly grow. For late Sargassum thunbergii, Above 10 ug/Lof Cu2+ concentration, growth of young sporophytes were seriously inhibited. 1ppb of Cu2+ concentration accelerated the growth. 50 ug/L and higher concentrations of Cu2+ made the young sporophytes grow slowly or cease to grow. Due to the special structure and function characteristics, rhizoid was not sensitive to Cu2+. At the beginning of Cu2+ treatment, rhizoid still presented fast growed.