Gas metabolism and fatty acid synthesis were studied in Mucor rouxianus by inoculing in various gas phase. This organism grown aerobically showed comparatively small Q_<02>/Q_<co2> value in endogenous respiration．But the value became bigger than 1.00 in case glucose added exogenously to this organism. In cells of M. rouxianus aerobically glown,〔fatty acid mg/dry wt. mg〕value reached to about 11%. Fatty acids constituting fat, included in the cells were lauric acid. (C_<12>), myristic acid(C_<14>), palmitic acid(C_<16>), stearic acid(C_<18>), oleic acid (C_<18:1>), and linolic acid (C<l8:2>). These higher fatty acids were found more in cells aerobically grown. But in cells anaerobically grown by carbon dioxide，those higher fatty acids were little found except myristic acid, palmitic acid，and palmitoleic acid.