Nitrilase (NLase) was covalently immobilized on modified Relizyme supports or adsorbed on montmorillonite K-10 or entrapped in polyvinyl alcohol hydrogel. Although 80-90% of initial loaded protein was immobilized, however, unsatisfactory activity recoveries was obtained in both covalent immobilization and adsorption studies. Entrapping NLase in polyvinyl alcohol allowed us to obtain an immobilized NLase with 80% activity recovery and 100% initial protein recovery. The characterization studies showed that the free and entrapped NLase samples had both maximum activity at pH 7.5 and 30 degrees C. The free nitrilase completely lost its initial activity at 30 degrees C after 24 h pre-incubation. However, the entrapped NLase retained 60% of its initial activity under the same conditions. Acrylonitrile with a initial concentration of 0.1 M was all converted to acrylic acid by entrapped NLase in 30 min whereas the same yield was achieved by soluble enzyme in 60 min. The entrapped NLase retained 84% of its initial activity after 15 reuses for the hydrolysis of acrylonitrile. These results show that the entrapped NLase can be of great interest as a biocatalyst to synthesize acrylic acid under mild reaction conditions.