In order to understand the effect of nitrogen sources on the growth and toxicity of harmful dinoflagellate Alexandrium tamarense, four nitrogen sources (nitrate, ammonium, urea and glycine) were added into artificial seawater enriched with F/20 and cells were batchcultured at 20 oC and 200 μmol photons·m^-2·s^-1. Cells of A. tamarense at exponential phase were collected to test the acute toxic effect on zebrafish embryo in 48 hours. The results showed that four nitrogen sources were all utilized by A. tamarense, but the growth rate was different, being ammonium (0.25 d^-1) > nitrate (0.20 d^-1) > urea = glycine (0.12 d^-1). However, the pigment contents were not influenced. Compared with the control group (embryo medium), the rude extract of A. tamarense at 2 ×10⁴ cells·mL^-1 had significantly teratogenic effects on the zebrafish embryos, resulting in embryo coagulation, developmental retardation, vitelline membrane rupture, yolk sac edema and tail bending. When the cell density increased to 8×10⁴ cells·mL^-1, the toxicity increased accordingly, moreover, a significant difference was found among the four nitrogen sources, showing nitrate > urea = glycine > ammonium. In summary, A. tamarense can maintain relatively high growth rate and make algal blooms outbreak continuously regardless of environmental changes, which threatens the ecological environment in coastal areas.