Viable hybridoma cells were encapsulated. The capsules were formed in one step by placing a drop of cell suspension mixed with negatively charged carboxymethylcellulose (CMC) into a positively charged chitosan solution through the interpolymeric ionic interaction between two oppositely charged polymers. These capsules were found to have a mean diameter of about 1. 5 mm and wall thickness of 3 μm. The cells grew in the capsules using supplemented DMEM/F12 (four kinds of growth factor). The maximum cell density in encapsulating cell culture reached 1 × 107 cells/ml, 10 times higher than that obtained in the free cell culture. The maximum monoclonal antibody concentration in the free cell culture was 15μg/mL, but that in the capsule was 45μg/mL The antibody produced by the cell was concentrated about four times higher inside than outside of the capsules.