Cigarette smoking, aromatic amines and ionizing radiation are known carcinogens of bladder cancer. NAT2 genotype might play a role in bladder cancer carcinogenesis. This hospital-based, case-control study was conducted in Kaohsiung, Taiwan, which neighbors the high incidence region of bladder cancer in the black-foot disease area. A total of 103 cases with diagnosed bladder cancer were collected. For each case, 1 control was selected from the same hospital. A structured questionnaire was applied for all cases and controls. DNA was extracted from peripheral blood cell. The ASO-PCR/RFLP technique was used to determine the NAT2 genotype. For bladder cancer, the significantly excessive risks were observed in regular drinkers (OR = 2.74, 95% CI = 1.28–5.87) and residents of the black-foot disease endemic area (OR = 7.53, 95% CI = 2.16–26.33), and interaction of regular drinking and slow type of NAT2 (OR = 18.04, 95% CI = 2.28–142.80). We suggested that NAT2 genotype might play a role of effect modifier in bladder cancer carcinogenesis.