Structure-guided microtuning of an Aspergillus usamiiepoxide hydrolase was executed. One mutant, A214C/A250I, displayed a 12.6-fold enhanced enantiomeric ratio (E= 202) toward rac-styrene oxide, achieving its nearly perfect kinetic resolution at 0.8 M in pure water or 1.6 M in n-hexanol/water. Several other beneficial mutants also displayed significantly improved Evalues, offering promising biocatalysts to access 19 structurally diverse chiral monosubstituted epoxides (97.1 – ≥ 99% ees) and vicinal diols (56.2–98.0% eep) with high yields.