The endocrine-disrupting chemical bisphenol A (BPA) has attracted attention because of its estrogenic activity and its extensive environmental distribution. The objective of this study was to investigate the physiological response of the alga Cyclotella caspia , a dominant species isolated from Futian Nature Mangrove Reserve, Shenzhen, China, to BPA at different concentrations (4, 6, 8, 10 and 12 mg l -1 ). We studied the effects of BPA on biomass, growth rate, chlorophyll (chl) a content, cellular morphology, and superoxide dismutase (SOD) activity of C. caspia . The effective concentration of BPA that inhibited algal growth by 50% at 96 h was 7.96±0.23 mg l -1 . Algal biomass, growth rate and chl a content decreased with increasing BPA concentration. BPA concentrations greater than 6 mg l -1 strongly inhibited cell division, significantly increased cell volume, and caused cellular inclusions to appear. SOD activity increased with the BPA concentration, but decreased with prolonged exposure time, showing a dynamic process from induction to inhibition. Our results provide baseline information for the development of marine ecotoxicology and physiology theories concerning BPA.