Simple SummaryWe developed a method to detect a single-point mutation in an obese gene in a mouse research model. The method is quick, easy to conduct, and suitable for obesity and diabetes-related research, especially in settings with constrained resources to identify and differentiate wild-type mice from mice carrying a gene mutation.Due to spontaneous deficiency in leptin, ob/ob mice are one of the most commonly used experimental animal models in diabetes research. In this study, we reported a quick and easy-to-conduct genotyping method using tetra-primer amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) to differentiate mice with a mutated allele from the wild-type genotype. The amplicon patterns of different genotypes are clearly visible and distinguishable on 1.5% agarose gel. This method can serve as a valuable tool to differentiate genotypes for breeding purposes, to maintain animal colonies, control the available space in the animal facility, and identify appropriate individuals for animal experiments.