The mode of growth and cellular division during synchronous culture has been studied in three strains of Chlorella ellipsoidea with different susceptibilities to low temperature. Cells of the strain T. I., which has little or no susceptibility to low temperature, completely divided only when the illumination was interrupted at the L_3 stage (ripening phase in the life cycle). When the L_3 cells were incubated in the dark, they divided into four daughter cells (Dn) with homogeneous size, while they were incubated in the light, their daughter cells were various in their size. The beginning of cell division in the light was later than that in the dark at the L_3 stage. However, the time required for complete cell division in the light was the same as that in the dark. These results are similar to those reported by Tamiya et al. The culture for the first cycle was subjected to a 23-hr light-12-hr dark regime. Good synchronization of algal cells was obtained after a second or a third cycle of 13-hr light-7-hr dark regime. The strain IAM C-102, which is sensitive to chilling injury, was different from the strain T. I. in the time required for growth and cell division. The time required for cell division in the light was shorter than that in the dark. The culture for the first cycle was subjected to a 23-hr light-12-hr dark regime. Good synchronization of algal cells was obtained after a second or a third cycle of 14-hr light-8-hr dark regime. The s train IAM C-27, which becomes hardy during low temperature treatment, remarkably differed from two strains in the mode of growth and cellular division. The cells at the ripening phase in the life cycle did not divide completely after 60 hrs incubation in the dark. They completely divided only when the illumination was continued until fully ripened stage. To obtain good and repetitive synchronous culture, the illumination was continued until 30 percents cells divided. The daughter cells obtained in this manner were homogeneous in their size. The time reqired for cell division in the dark was much slower than that in the light. The culture for the first cycle was subjected to a 40-hr light-20-hr dark regime. Good synchronization of algal cells was obtained after a second or a third cycle of 28-hr light-l4-hr dark regime.