To efficiently obtain the subject compound for intermediates of medicines and agrochemicals by reduction action of a plant cell by adding a specific β-ketocarboxylic acid ester to culture medium of a plant cell and repeating culture a plurality of times for a prescribed period.

A process adding a β-ketocarboxylic acid ester represented by the formula (R1 is a lower alkyl; R2 is H, a lower alkyl or an allyl) (e.g. ethyl α-methyl-β-ketobutanate) to culture medium of a plant cell (e.g. liverwort cell) and then culturing the plant cell for a prescribed period is repeated plural times to afford a first cycle and at the point of time when the first cycle finished, the culture medium is exchanged with the new culture medium and further, the next second cycle is carried out to efficiently provide the objective β-hydroxycarboxylic acid ester important as an intermediate for various medicines or agrochemicals or an intermediate in synthesizing useful natural compounds based on reduction action of a plant cell in a high yield.