In order to test the feasibility of using calcium alginate-entrapped hybridoma cells for IgM production, HO-22-1 hybridoma cells entrapped into calcium alginate beads with varying alginate concentrations were cultivated in spinner flasks. It was observed that IgM produced by the entrapped cells could diffuse out of the calcium alginate beads regardless of alginate concentration tested (0.8-2.5\%). Since the increase in alginate concentrations showed an adverse effect on cell growth and maximum cell concentration, the use of lower alginate concentration was desirable for higher volumetric monoclonal antibody (MAb) productivity. However, the value of specific MAb productivity, $q_{MAb}$ in 0.8\% alginate beads was approximately a half of that of $q_{MAb}$ in free-suspended cell culture. Therefore, further efforts was made to improve the $q_{MAb}$ of the entrapped cells in 0.8\% alginate beads. The $q_{MAb}$ of the entrapped cells was improved by employing frequent medium exchange. Further, when the entrapped cells in 0.8\% alginate beads were cultivated in a repeated fed batch mode, the reduction of serum concentration in the medium from 10\% to 1\% did not decrease the volumetric MAb productivity. Taken together, the data obtained here showed the feasibility of using calcium alginate entrapped hybridoma cells for IgM production.