Poly(vinyl alcohol) (PVA) hydrogel beads crosslinked with boric acid have been widely utilized for microorganism immobilization. However, a drawback of the method for preparing conventional PVA-boric acid beads is that microorganisms enclosed in the PVA matrix are drastically damaged by boric acid during the bead preparation process. In the present study, we utilized sodium sulfate as an inducer for crosslinkage of PVA for fabricating microorganism-enclosing PVA hydrogel beads to avoid the drastic decrease in cell viability caused by saturated boric acid solution. First, PVA was crosslinked by boric acid for a short time. Subsequently, the molecules were further crosslinked using sodium sulfate. X-ray diffraction analysis indicated that sodium sulfate promoted crystallization of PVA, which contributed to gelation of PVA solution. Moreover, the toxicity of sodium sulfate to Saccharomyces cerevisiae was lower than that of boric acid. The stability in water of the PVA-sodium sulfate beads was superior to the stability of PVA-boric acid beads. The ethanol fermentation rate of the PVA-sodium sulfate hydrogel beads enclosing the yeast cells was 2-3 times as fast as that of PVA-boric acid beads. The PVA-sodium sulfate beads could be reused 10 times in repeated ethanol fermentation tests. (C) 2010 Elsevier Ltd. All rights reserved.