According to the results measured the respiratory quotient of Saccharomyces cerevisiae with neutron radiation by manometric direct method, the respiratory quotient of them was stimulated at the dose(7$ imes$106N/$ extrm{cm}^2$/sec) of neutron radiation for 60 seconds, and was inhibited in each group irradiated at the high dose (7$ imes$108N/$ extrm{cm}^2$/sec) of neutron. Its physiological effects influenced on neutron had relations with respiratory quotient, reproductive rate and fermentation in the curve of normal logarithmic phase. The multiple reactions which appeared in yeast, indicated that a great deal of physiological function were closely correlated with the irradiated dosage of neutron. The kinds of free amino acid in yeast irradiated with neutron were different from those of unirradiated yeast. The activityof dehydrogenase system accelerated the metabolic function of yeast irradiated at some low dose of neutron. By this results, it may demonstrate that the fact which the phenomena obtained in the stimulation of neutron possess its character for several generation, is dependent on the theory of mutation. Subsequently, it seemed reasonable certain dominant type of microorganisms.