Previous studies showed that abscisic acid (ABA) play a role in oxidative and osmotic stress response of cyanobacteria cells. Whether it has function in metal stress response remains unclear. The effect of exogenous Abscisic Acid on Cu2+ -Stress resistance of bloom-forming cyanobacteria Microcystis aeruginosa was studied in this paper. The results showed that 20 mg. l-1 exogenous ABA can effectively enhance the resistance ability of Microcystis aeruginosa cells to Cu2+-stress at the concentration of 0.25 mg.l-1. Exogenous ABA can restore the growth inhibition by elevating chlorophyll a, phycocyanin and allophycocyanin protein content in Cu2+ -stressed cells. ABA helps absorbing more metal ions to decrease its toxicity by inducing solvable protein and cellular polysaccharides biosynthesis. By promoting the Superoxide Dismutase and Glutathione Peroxidase activities, exogenous ABA can effectively help scavenge the excess superoxide radicals in the cells caused by Cu2+ -Stress. These results indicated that ABA might also play important role in metal-stress response and resistance.