To provide a method for preparing a cell of a recombinant microorganism having a gene encoding an enzyme easily deactivated by the contact with oxygen or a superoxide, or a culture liquid containing the cell by stably expressing an activated enzyme.

The method for preparing the cell or the culture liquid containing the cell of the recombinant microorganism having the gene, encoding the enzyme easily deactivated by the contact with oxygen and/or the superoxide, comprises culturing the recombinant microorganisms obtained by expressing the gene in a host microorganism having oxygen-consuming ability and/or superoxide-removing ability in a culture liquid to which the recombinant microorganisms are inoculated while feeding oxygen and regulating the amount of the fed oxygen so that the concentration of the dissolved oxygen in the culture liquid at the finish of the culture of the microorganisms may be ≤0.5 ppm, and collecting the cell or the culture liquid containing the cell.