A unicellular alga with high growth rate under hetrotrophic growth conditions was isolated from soil and identified as Chlorella sorokiniana. Isolated unicellular algae were highly resistant to heavy metals such as Cd²⁺, of which the minimal inhibitory concentration was 4 mM. Algae were capable of taking up the heavy metal ions Cd²⁺, Zn²⁺ and Cu²⁺at 43.0 µg, 42.0 µg and 46.4 µg per mg dry weight, respectively. Growth inhibition of Oryza sative shoots by 5 ppm Cd²⁺ in water culture medium was completely prevented by addition of 0.25 mg of Chlorella cells. These results indicate that this isolate is potentially useful for phytoremediation by preventing environmental dispersion of heavy metals. The metal-binding proteins of C. sorokiniana are induced in the presence of cadmium. A novel cadmium-binding protein in C. sorokiniana cultured in 100 mg/l cadmium ions for 4 days was isolated and characterized. The molecular weight of the purified protein was determined to be 11.5 kDa by SDS-polyacrylamide gel electrophoresis. The cadmium binding capacity of the purified protein was 119 µg/mg. The involvement of thiol co-ordination in metal ion binding was confirmed by measuring the UV spectrum. The internal amino acid sequence was isologous with that from histidine triad protein from Bordetella brochiseptica, zinc finger protein from Xenopus laevis and nickel-cobalt-cadmium resistance protein from Alcaligenes xylosoxidans.