Abstract: A Spirulina platensis mutant PNK-2 had been bred from S.platensis mutants which had been induced by space flight. PNK-2, with good quality and high yield, suits for out-door mass production. Comparing with the initial strain ST-6, the helix number of PNK-2 was 12~ 18, average length of algae body, thread pitch, helix width, diameter of trichome and the rate of large-scale production were 764.31, 52.98, 18.75, 6.02 m and 10 g(m2d)-1, respectively, and the increase rate were 166.52%, 5.88%, 8.19%, 12.31% and 22.89%, respectively. The content of protein, chlorophyll, -carotene and phycocyanin in PNK-2 were 69.57%, 1.01%, 0.16% and 14.70%, respectively; and the increase rate were 8.31%, 8.60%, 6.67% and 6.68%, respectively. The -linolenic acid content of PNK-2 was 0.63%, reducing 3.08%. The results showed that PNK-2 was a new S.platensis strain with good quality and high yield.