Abstract: Two photoinhibition-resistant mutants, (Sp) AIp-90010 and (SP) AIp-90011were selected after inducing the Spirulina platensis initial strain (Sp)IS-90010 with ～⁶⁰Co-γ irradiation,and their general morphology ,physiological features and biochemical composition were studied comparatively.There are some morphological differences between the initial strain and the mutants.The filaments of two mutants show much shorter length and fewer numbers of the helix than of the initial serain.The initial strain is sensitive to high light, while two mutants are obviously resistant to photoinhibition.Under 13000 lx, the generation time of the initial strain.(Sp) AIp-90010, (Sp) AIp-90011 is 29.4、20.8 and 22.2 h,respectively.(Sp)AIp-90011 has similar photosynthesis and respiration to the initial strain, but (Sp)AIp-90010 obviously has higher photosynthetic rate and lower respiration.The mutants and the initial strain belong to suitable middle-temperatured strains, and their optimal temperature is 28℃.Each of the mutants exhibits the same adaptable temperature range (23～33℃) and salt tolerance as the initial strain.There is no apparent difference in protein content and amino acid composition among two mutants and the initial strain,while the water-soluble polysaccharide in (Sp)AIp-90011 decreases by 40% and it in (Sp)AIp-90010 increases by 60% compared with the initial strain.