Abstract: Additions of 0.005-0.03ppm cupric ion enhanced the growth of the nitrogen-fixing blue-green algae in the culture medium.The optimum Cu++concentration for growth is 0.01 ppm for mixed culture of Anabaena species and monoculture of Anabaena azotica;for mono- culture of Anabaena variabslis,the optimum cuncentration is 0.03ppm.The optimum range of Cu++ concentration is widen for algae in tanks with soil substrates than for algae in tanks without substrates.