Macroporous poly(vinyl alcohol) foam with epichlorohydrin as a crosslinking agent was investigated. The average molecular weight between crosslinks, crosslinking density, and mesh size were determined through the equilibrium swelling theory. The characterization of foams with different crosslinking ratios was also investigated through the testing of the thermal properties, specific surface areas, and diffusion coefficients. The biomass densities and activity yields were measured by detection of the protein concentration and oxygen uptake rate. Thermogravimetry and differential scanning calorimetry tests showed an increase in the thermal stability and a decrease in the polymeric crystallinity with increasing crosslinking ratio. The biomass densities increased with increasing crosslinking ratio, with the highest value shown at 0.0638 +/- 0.0093 g of volatile suspended solid (VSS)/g of carrier. However, the activity yields decreased with increasing crosslinking ratio, with the highest value at 69.38%. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2732-2739, 2010