The immobilization method of Lactobacillus casei cells was investigated using alginate capsules that possess an interphasic membrane and a liquid core. The capsules were found to offer more space for cellular growth than gel-core beads, which resulted in 1.5-fold higher cell concentration than in the latter; however the Ca-alginate structure was unstable during repeated batch fermentations for lactic acid production. Ba-alginate capsules were chemically and physically more stable than Ca-alginate capsules in phosphate and lactate solutions. Attempts were also made to use various hardening agents to stabilize the structure of the Ba-alginate capsules. It was found that the treatment with a mixture of chitosan and BaCl2 solution gave the best results for hardening. Finally, stable lactic acid production was possible with a productivity of more than 2.7 gl(-1)h(-1) by L. casei cells immobilized in chitosan-coated Ba-alginate capsules. The cell leakage from the capsules was maintained relatively low during batch fermentations.