PURPOSE: To enable to produce a unicellular protein in a high yield by aerobically culturing a new yeast having a growth potential under methanol in an aqueous culture medium containing an oxidized hydrocarbon as a carbon source and an energy substrate.

CONSTITUTION: This new yeast strain: Hansenula polymorpha NRRL-Y-11432 (FRI-5684), having a growth potential under methanol is prepared. The new yeast strain having a logarithmic phase for a long period and having a methanol-metabolizing ability is cultured in an aqueous culture medium containing an oxidized hydrocarbon (e.g. methanol or glucose) as a carbon source and an energy substrate under an aerobic fermentation condition. The produced microorganism cells are separated and recovered as a unicellular protein material. Thereby, the yeast can be cultured in a high cell density, and the unicellular protein can be produced in a high yield.