Abstract:The production of toxin is a feature in red tide. More than 70 species of microalgae produce toxins. As a secondary metabolite, the synthesis of algal toxin may be considered as an inhibition or rejection response to other phytoplanktons in the competition among communities and species. There is little understanding about the synthesis pathway of these toxins because the factors （algal species, sources, environment, conditions, etc.） that affect the production of toxin are complicated. In this review, the following aspects in studies on algae which from red tide are presented： ecological significance of red tide algae producing toxins, factors affecting the production of toxins by algae, possible biochemical pathway of toxin synthesis, and molecular aspects of toxin biosynthesis in study of marine algae.