PURPOSE: To accumulate β-carotene in cells of limnetic green algae and produce the subject β-carotene by culturing the limnetic green algae in a culture solution containing a specific amount of an alkali meta halide.

CONSTITUTION: For example, cells of limnetic green algae belonging to the genus Chlamydomonas, etc., are cultured in a TAP culture medium, etc., and then in a culture medium containing an alkali metal halide (preferably sodium chloride) at ≥0.15mol concentration to accumulate β-carotene in the cells (in an amount of preferably ≥0.1% based on the weight of the cells) and produce the objective β-carotene.