Abstract: Grown in BG11 liquid medium with 0.05 mol/L chloride, nitrate, sulphate and phosphate of K+, Na+ and ammonium ion for 2 days, the cells of Anabaena sp. 595 inflated, vacuolized and performed longitudinal or unequational division; the trichomes fragmented and the number of heterocysts increased. And special contracted granules appeared in the cells when they were treated by ammoniumions. In comparison, the cells were less affected by Ca2+ and Mg2+. While cultured in the medium containing 0.01mol/L NaCl for long-term, the cells exhibited cyclic diff erentiation. It inflated and vacuolized firstly, then the pigment expanded and vacuolization disappeared, finally, the cell divided to normal size. In fact, the inflation and vacuolization appeared again in the following days, so the cycle continued.