A microbioreactor (upper width = 433 mum, lower width = 296 mum, depth - 91 mum) was designed on a silicon wafer by wet chemical etching, and the resulting channel was seated with a glass cover by an anodic bonding technique. Biodegradation of an environmental pollutant (p-chlorophenol) was conducted using laccase in the microreactor. The enzymatic reaction smoothly proceeded in the microreactor, and the reaction rate was enhanced 400-fold compared to that of an ordinary bulk reaction. It was found that the enzyme exhibited high stability in the microreactor, which allows recycling the enzyme solution. The biodegradation yield attained 90% when several microreactors were connected in series.