The toxicity of naphthalene to Chlorella vulgaris was studied under nitrogen (N)-, phosphorus (P)-enriched and NP-starved condition. Results showed that naphthalene was less toxic under NP-starved condition. The inhibitory rates were less than 15.3% to C. vulgaris during 7 days exposure with the initial concentrations of naphthalene at 5, 10, 50, 100 mg/L, respectively under N,P-starved condition, while they were 7.5-72.3% under N,P-enriched condition. The malondialdehyde (MDA) content indicated that there was no oxidative damage to algae when the initial concentration of naphthalene was less than 10 mg/L, and oxidative damage exhibited to algae at 50-100 mg/L of naphthalene under N,P-starved condition. Naphthalene induced oxidative damage to the algae at all tested concentrations (5-100 mg/L) under NP-enriched condition. The results indicated that there was a negative relationship between the special growth rate (SGR) and naphthalene concentration in the medium. Under N,P-enriched condition SGR of the control decreased slowly from 0.669 to 0.186. However, SGR of the naphthalene treated group decreased sharply during the first 2-3 days when the dissolved concentration of naphthalene was above 0.1 mg/L, and then increased gradually with the evaporation of naphthalene. (C) 2010 Elsevier B.V. All rights reserved.