A genetic study on aldehyde dehydrogenase 2 (ALDH2) genotype was performed in a rural area of Khon Kaen province, northeastern Thailand. One hundred and twenty four fingernail specimens of probable non-alcoholics were obtained from unrelated male villagers 18-65 years old. The alcoholism screening test named "the Michigan Alcoholism Screening Test-Thai version (MAST-T)" was used for inclusion of probable-non-alcoholic subjects. Genomic DNA was extracted from clipped fingernails and ALDH2 genotypes were determined by PCR, Ksp 632I, digested and polyacrylamide gel electrophoresis. Most of the subjects (91.1%) were of the normal homozygous genotype (ALDH2*1/ ALDH2*1), 8.9%, heterozygous genotype (ALDH2*1/ALDH2*2), and none of them were the mutant homozygous genotype (ALDH2*2/ALDH2*2). Gene frequencies of ALDH2*1 and ALDH2*2 alleles calculated from the genotype frequencies were 0.956 and 0.044, respectively. Deviation from the HardyWeinberg' s equilibrium was not statistically significant. The present study confirms the high frequency of ALDH2*1 gene (0.950-0.956) in non-alcoholic Thai population. Interestingly, the ALDH2*2 gene is not prevalent among Thai population compared with the Japanese and Chinese, though, they are of Mongoloid origin. The information on ALDH2 gene frequency of Oriental populations and Caucasoids were discussed.