The STR locus HUMTH01 was studied in 110 unrelated Thais from the area of Chiang Mai in North Thailand. By using PCR and vertical PAGE, six alleles were identified and the frequencies ranged from 0.005 to 0.400. The allele frequency distribution in this population showed significant differences from a Japanese population and other ethnic populations but was similar to Asians in the USA and Australia. The genotype distribution meets Hardy-Weinberg expectations. The average power of exclusion (in no-parent and one-parent cases) and the discriminating power (DP) were calculated to be 0.3020, 0.4761 and 0.8722 respectively.