Crude enzyme extracted from soybean was used to convert isoeugenol into vanillin. The effects of several factors on the bioconversion were studied. Conversion was affected by the amount of substrate and was also improved by the addition of absorbents, among which powdered activated carbon was the best. The effect of H2O2 concentration on the conversion was also studied. The optimum concentration of H2O2 was 1% (v /v). With 10 g/L of powdered activated carbon and 0.1% H2O2 added, vanillin reached a maximum concentration of 2.46 g/L after 36 h, corresponding to a molar yield of 13.3%.