Abstract: In order to find the toxic effects of 1-Naphthol on the primary products in the aquatic ecosystems, the effects of 1-Naphthol on the biomass, chlorophyll a, Malondialdehyde (MDA), soluble protein of Chlorella vulgaris was carried out. The results showed that 1-Naphthol could inhibit the growth of Chlorella vulgaris, and after 7 days, the biomass of Chlorella vulgaris exposure to 1.0, 3.0, 6.0, 12.0, 18.0 mg/L was 60.26%, 48.15%, 41.32%, 28.59%, 27.10% of the control respectively. After 7 days of exposure to 1-Naphthol (0, 1, 5, 10 mg/L), the chlorophyll a content decreased with the concentration of 1-Naphthol increasing, the MDA content increased with the concentration of 1-Naphthol increasing, the content of soluble protein increased firstly and then decreased with the concentration of 1-Naphthol increasing. 1-Naphthol was high toxic to Chlorella vulgaris, and it could inhibit the growth of Chlorella vulgaris and therefore could decrease the primary product of aquatic eco-system.