Abstract: Cultures of Anabaena sp. 7120 were carried out in nitrogen free BG 11 medium in an orbital shaker at 130 r/min and 30℃ at a light intensity of 160 μE m-2 s-1 unless otherwise specified. Various concentrations of organic carbon compounds were contained in the medium to examine their effects on the growth of Anabaena sp. 7120 cells as indicated by the cell density and the chlorophyll concentration. Glucose was shown to be able to improve cell growth markedly. With the glucose concentration varying within a range from 0 to 30 g/L, the maximal cell density in mixotrophic growth was able to reach 3.4 folds of that in photoautotrophic growth. Glucose was utilized to a limited extent in mixotrophic cultures. Cell growth at various light intensities indicated that the saturation light intensity for mixotrophic growth with a glucose concentration of 3 g/L was around 80 μE m-2 s-1. Acetate was found to impede cell growth to some extent when examined within a concentration range from 0 to 1.5 g/L. Sucrose, ethanol and glycerol exerted slight influence on cell growth, whereas lactate, citrate, glutamate and glycine inhibited cell growth seriously. Glucose, acetate, sucrose, glycerol and ethanol did not cause significant changes in photosynthetic oxygen evolution and dark respiratory oxygen consumption while lactate, citrate and glutamate destroyed these activities. Anabaena sp. 7120 did not exhibit heterotrophic growth on glucose in complete darkness or light activated heterotrophic growth on glucose with a daily pulse of light of 5 min of 160 μE m-2 s-1. However, comparison of cell growth in the presence of 10-5 M DCMU with and without glucose in light suggested that slight photoheterotrophy may exist.