Abstract: In this paper, it was studied that the effects of naphthalene and its derivants ( naphthalene, 1-naphthol, 2-naphthol and 1-naphthylamine) on growth, chlorophyll a content, intensity of photosynthesis and respiration of C.vulgaris.Naphthalene, 1-naphthol and 1-naphthylamine in low concentrations stimulated the growth of Chlorella vulgaris, but these chemicals in higher concentrations inhabited its growth significantly.2-naphthol inhabited the growth in all concentrations (1 to 40 mg/L) tested.The EC50 of naphthalene, 1-naphthol, 2-naphthol and 1-naphthylamine were 98.06, 11.87, 13.39 and 6.95mg/L, respectively.The toxic effects of naphthalene and its derivants on chlorophyll a content and intensity of photosynthesis were stronger than those of growth.Naphthalene and 1-naphthol in low concentrations, intensity of respiration of C.vulgaris were of stimulative effects, but at higher concentrations, the intensity reduced.On the contrary, 2-naphthol did not affect intensity of respiration of C.vulgaris at low concentrations, the intensity increased significantly.1-Naphthylamine reduced respiration intensity of C.vulgaris, but then increased slowly.