Abstract: The effects of low temperatures on some physiological and biochemical characteristics of Nostoc sphaeroides kütz.were studied.Results showed that the growth of N.sphaeroides was inhibited by low temperatures,most severely,it was nearly ceased at 2℃ and 5℃,while,at 10℃,and normal growth was attained after a prolonged lag phase.Change of photosynthetic activity(represented by Fv/Fm) in N.sphaeroides under low temperatures was similar to that of the growth.The permeability of cell membrane could maintain a low level at initial stage,and then increased with prolonged low temperature treatment.With lower temperature stress,the contents of total sugar and reducing sugar increased to variant extents.Content of soluble protein in N.sphaeroides kept at a low level when it was subjected to chilling stress.All the results indicate that the growth and photosynthetic activity of N.sphaeroides could be inhibited by low temperature,however,the algal cells can also show abilities of chill-resisting,adapting to low temperatures by membrane permeability regulating and chilling-adjusting substances(such as total sugars and soluble sugars) synthesizing.