Abstract: Spirulina platensis was induced by ultraviolet irradiation as a mutagen. Two good mutants,M1-3 and M5-1,were selected. M5-1 was bigger than PS(Paprent Strain),and M1-3 was thinner and much longer with its spiral number of one filament being over 40;The growth and photosynthetic O2 evolution rates of two mutants were higher than those of PS obviously. Phycocyanin content in M1-3 was 20.2% higher than those of PS. The two mutants had more long carbon chain polyunsaturated fatty acids. The M1-3 contained 4.93% arachidonic acid(20∶4),and M5-1 contained 2.49% EPA(20∶5)in the total fat. The antitoxic abilities of two mutants to toxic ions,NH4+ and Zn2+ were different from PS also.