Cells of Saccharomyces cerevisiae (ATCC 24858) were encapsulated in the calcium alginate membrane and cultured. Swelling of the capsule was prevented by adding 0.2 g CaCl2 to 1 L growth medium. The dry cell concentration based on the inner volume of the capsule reached 309 g/L, which was much higher than could be obtained by cell entrapment. Ah the cells remained inside the capsule during the cultivation. The flux of CO2 through the capsule membrane increased approximately twice by adding a nonionic surfactant to the CaCl2 solution during the step of capsule formation.