We developed two nanoimmobilized biocatalyst systems of thermally unstable Mugil cephalus epoxide hydrolase (McEH) for enantioselective resolution of racemic styrene oxide in aqueous buffer. The recombinant and purified McEH enzyme was immobilized onto magnetic nanoparticles (Mag-NPs) via a two step process of enzyme precipitation and crosslinking. McEH enzyme was also adsorbed, precipitated, and cross-linked in/on polyaniline nanofibers (PANFs). The residual relative activity of free McEH, defined as the ratio of residual activity to the initial activity, was 8% after incubation at 30 degrees C for 80 h while those of McEH immobilized onto Mag-NPs and in/on PANFs were 15% and 33% in the same condition, respectively. McEH immobilizations onto Mag-NPs and in/on PANFs could be reused in seven repetitive batch reactions for enantioselective hydrolysis of racemic styrene oxide to prepare (S)-styrene oxide with 98% enantiomeric excess (ee) while retaining greater than 40-50% of their initial activity.