Nutritional requirements for the growth of Cellulomonas flavigena were studied. C. flavigena grew well on cellulose when 0.005% or more of yeast extract was present in the growth medium. The growth factor in yeast extrct was, in part, thiamine and biotin. Amino acids had little effect on the growth on the organism. The extent of growth on yeast extract was much higher than that obtained on those vitamins, which indicates the presence of growth factors in yeast extract besides the vitamins, among the carbohydrates tested, the organism grew best on glucose and galactose, and the optimum N/P ratio was within the range of 0.75~3.17.