PURPOSE: To increase the production of ergosterol, remarkably, by culturing yeast in the copresence of a source of isoprenoid compound precursor and one or more compounds selected from acetoacetic acid esters and nonionic surface active agents.

CONSTITUTION: Ergosterol-producing yeasts are cultured aerobically in a medium comprising a conventional yeast culturing medium added with a source of an isoprenoid compound precursor, e.g. acetic acid, leucine, etc., and one or more compounds selected from acetoacetic acid esters such as ethyl acetoacetate, methyl acetoacetate, etc. and nonionic surface active agents such as sorbitan monolaurate, polyoxyethylene sorbitan trioleate, etc. The objective compound can be separated from the yeast cells.