1. In industrial tests using a fermenter of two tons in capacity, the authors obtained nearly the same results as the previous findings with a 100 liters plant ; namely with a medium consisting of cane molasses and peptone, or cane molasses and fish meal, riboflavin yields in the method of feeding were of 127-216mg%. 2. From cost accounting with necessary industrial plans, it was concluded that the economical scale of production should be over 500 kg of riboflavin per month, and that it is premature to materialize such methods as the amount of consumption of riboflavin is not so high in Japan.