Abstract: This study investigated nutrients component, photosynthetic activities, pigments components, polysaccha-ride contents and photosynthetic activities during the colony size variation of Nostoc sphaeroides. The result showed that the content of chlorophyll a and phycobiliprotein decreased with increased colony particle size. The maximum content of carotenoid was occurred in colonies with particle size 4.85 mm; the phycobiliprotein contents was the highest in colonies with particle size 0.77 mm; the maximum content of polysaccharide was occurred in colonies with particle size 3.03 mm; the proportion of phycocyanin/chlorophyll a, phycoerythrin/chlorophyll a and allophycocyanin first increased and then decreased with the enhanced colony particle size; the maximum potential photosynthetic capacity (F_v/F_m) reduced with the increase of colony particle size. Colonies with smaller size were more tolerant to high light intensity than larger ones, and the high rate of cyclic electron transport of the colonies with large particle size can dissi-pate excess energy to counter the damage caused by the high light. The growth of Nostoc sphaeroides shows size effect and the cell component and photosynthetic activities mediate colony size variation, which are important to concern the mass of start culture and the harvest time of Nostoc sphaeroides.