The effects of strontium on growth, peroxidation and antioxidative enzymes have been investigated in Dicrateria inornata. The marine microalga grew at all treatment concentrations of strontium, but samples exposed to 512 and 2048 mg strontium l–1 were inhibited by 15.9% and 51.0%, respectively, compared to controls. Among the responses to added strontium, accumulation of malondialdehyde increased significantly at 2048 mg strontium l–1 and was 1.23 fold higher than in controls, and protein content increased at low external concentrations but decreased above 128 mg l–1. In the case of antioxidant enzyme activities, SOD, CAT and GPX activities increased by 85.7, 19.8 and 74.4%, respectively, at 2048 mg strontium l–1 compared to the control. The GSH content increased by 5.2% at 512 mg l–1 and by almost 100% at 2048 mg l–1 strontium compared to controls.