A new microorganism immobilization method involving gelation of anionic polyurethane has been developed. Nontoxic synthetic anionic polyurethane was used, which provides greater mechanical strength than do natural polymers. Similar to the formation of Ca-alginate gel beads, this method has the advantage of easy preparation. Gel beads are formed only by dropping the anionic polyurethane emulsion into a calcium chloride solution. The feasibility of the proposed immobilization method was tested by an ethanol production process with baker's yeast (Saccharomyces cerevisiae). The result verified that the anionic polyurethane entrapped-cell method developed in this study has great potential for a variety of applications such as biological processes and biological wastewater treatment. (c) 2005 Wiley Periodicals, Inc.