One hundred and forty-five ESCC patients and 352 controls were recruited from three hospitals in Taiwan to determine the association between esophageal squamous-cell-carcinoma (ESCC) and microsomal epoxide hydrolase (mEH) genotypes at Thy113His and His139Arg. Stratified by their exposures, the His113His genotype was a significant protective factor for ESCC in areca chewers and tobacco smokers. Stratified by His113 polymorphisms, the risk of contracting ESCC for participants with His113His who chewed areca and smoked was >50% less than for those with Thy113Thy. We suggest that the mEH His113His genotype can differentiate the association between smoking, areca chewing, and ESCC.