The immobilization of plant growth-promoting bacteria in biodegradable polymeric supports is effective in providing them with a suitable microenvironment for increased survival, compared to free bacteria, in agricultural land. In this study, we optimized the preparation parameters for bacteria-enclosing calcium alginate gel beads with a view to large-scale production. An emulsion system was used and the optimization was based on alginate bead recovery and entrapment efficiency of viable bacteria. Lactic acid bacteria were used as a plant growth-promoting bacteria. The optimized conditions were as follows: the concentration of calcium chloride in the aqueous phases was 1.1% (w/v), the volume ratio of alginate solution to total aqueous phases was 0.93, and the agitation time was 0.5-1.0 h. The mean diameter of the beads could be controlled (approximately from 100 to 300 mu m) by varying the agitation rate.