To provide more information on new algaecide with high efficiency, ecological safety and selectivity, effects of corn stem and leaves on the growth of Alexandrium tamarense were observed. The roles of microorganism in the inhibition were assessed. The inhibitory activities of different solvent extracts from the corn leaves were discussed and the potential antialgal chemicals in corn leaves were analyzed by GC-MS. Cornstalk is shown to have distinctly inhibitory effect on A. tamarense, and the inhibition of corn leaves is stronger than that of the corn stem. 0.5 g/L of the corn leaves inhibit A. tamarense remarkably in cell density of 1.69 x 10(6) cells/L. There are little differences in antialgal action between asepsis leaves and rude leaves, suggesting that some antialgal compounds from leaves may be responsible for the inhibition and that microorganisms from leaves have little effect on the inhibition. The petroleum ether and dichloromethane extracts from corn leaves are shown to have stranger inhibition on A. tamarense than ethyl acetate and n-butanol extracts. CC-MS shows that extracts with high inhibitory activities contain many fatty acids such as linoleic acid, linolenic acid, and palmitic acid, etc. These results suggest that corn leaves have some inhibitory effect on A. tamarense and fatty acids may be responsible for the inhibition.