Abstract: We studied the effect ofCu2+ stress atdifferent concentrations on the growth and physiological biochemical characteristics of Sargassum hemiphyllum by a semi-static test for 8 d. The results show that the relative growth rate (RGR) of thalli in the control increased innitially and then decreased with time; on the 8th day, the RGR of thalli was higher than that in the control only when Cu2+ concentration was 0.05 mgL-1. The physiological biochemical indices showed a fluctuation trend with time. On the 8th day, these indices of thalli at Cu2+ concentration of 0.01 mgL-1 had no significant difference with the control; when Cu2+ concentration was 0.05 mgL-1, thecatalase (CAT) activityand malondialdehyde (MDA) content were significantly higher than those in the control, and the other indices recovered to the control level. However, in Cu2+ 0.05 mgL-1 groups, chlorophyll a (Chl- a), carotenoid (Car) and soluble protein (SP) were lower than those in the control; the other indices were higher than those in the control. Compared with 0.25 mgL-1 Cu2+ group，1.25 mgL-1 Cu2+ group had more significantinfluence onbiochemical indices except MDA.. Therefore, appropriate concentration of Cu2+ ( 0.05 mgL-1) had positive effect on the growth and physiological biochemical indices of S.hemiphyllum, but there was negative impact on the growth and the ability of resilience of thalli when the concentration of Cu2+ was extremely high ( 0.05 mgL-1).