Thai Hom Mali Rice (THMR) is recognized for its premium quality in the global market. One of the significant problems of a decrease in the quality of THMR is an admixture of other rice varieties. To maintain the popularity of such rice by targeting the upper market, The Nation Bureau of Agricultural Commodity and Food Standards issued Thai Hom Mali Rice standards stating that must be Thai Hom Mali Rice not less than 92%. Several methods have been employed to enforce this standard and showed less possibility of detecting adulterants. However, DNA-based methods have been proven to purge the adulteration problem. This research reports that 5 SSR primers, RM213, RM336, RM337, RM474, and BV210145, were selected for genetic purity test in THMR. In addition, a simplified rice grain DNA extraction protocol by 0.1M NaOH solution in a single microcentrifuge tube. It was found that there was good DNA that was enough PCR analysis. Furthermore, the appropriate sample size for mixing seeds detection was evaluated at a confidence interval level of 95 percent.