Chlorella ellipsoidea cells were cultured in an iron, copper, zinc, manganese, molybdenum or boron-free medium. Physiological activities such as growth rate, reproduction, endogenous and glucose respiration, photosynthetic activity and biosythesis of chlorophyll of the micro-element definition cells were measured. It generally, growth rate, respiratory and photosynthetic activities, and biosynthesis of chlorophyll of the micro-element deficient cells decreased more or less, compared with those of the normal cells. The growth of the algal cells in an iron-free medium were retarded severely with the chlorosis, and the photosynthetic activity of the cells decreased remarkably even though the low content of chlorophyll in the cells owing to the iron-deficiency is considered. Therefore, it is deduced that iron takes part in the photosynthetic process itself, possibly by its participation in the photo phosphorylation coupled with electron transport. Respiratory activity of boron-deficient cells showed the most severe decrease whereas those of the molybdenum-deficient cells showed very slight decrease in spite of severe growth retardation.