Two species of marine microalgae, Isochrysis galbana 8701 and Skeletonema costatum, were exposed to low concentration of anthracene, and their cell density, contents of chlorophyll a, carotinoid and protein, and superoxide dismutase (SOD) activity were examined. It was showed that low concentration of anthracene (1.5-6.0 micrograms.L) could obviously stimulate the growth of these microalgae, and their protein, chlorophyll a, and carotinoid contents increased with increasing cell density. SOD of treated groups remained high activity, compared with the controlled group during the whole experiment.