Mixotrophic growth is one potential mode for mass culture of microalgae and cyanobacteria particularly suitable for the production of high value bioactive compounds and fine chemicals. The typical heterocystous cyanobacterium Anabaena sp. PCC 7120 was grown in the presence of exogenous glucose in light. Glucose improved the cell growth evidently, the maximal specific growth rate under mixotrophic condition (0.38 d(-1)) being 1.6-fold of that of photoautotrophic growth. Mixotrophy caused a variation in cellular pigment composition, increasing the content of chlorophyll a and decreasing the contents of carotenoid and phycobiliprotein relative to chlorophyll a. Fluorescence emission from photosystem II (PSII) relative to photosystem I was enhanced in mixotrophic cells, implying an increased energy distribution in PSII. Glucokinase (EC 2.7.1.2) activity was further induced in the presence of glucose. The mixotrophic culture was scaled up in a 15 L airlift photobioreactor equipped with an inner and an outer light source. A modified Monod model incorporating the specific growth rate and the average light intensity in the reactor was developed to describe cell growth appropriately. The understanding of mixotrophic growth and relevant physiological features of Anabaena sp. PCC 7120 would be meaningful for cultivation and exploitation of this important cyanobacterial strain.