Introduction: Diabetes mellitus is a chronic metabolic disorder characterized by elevated blood glucose levels. Over the past two decades, the prevalence of diabetes has been increasing rapidly in Mongolia. Although the national prevalence is not the highest in the region, it is relatively comparable to that of other Asian countries such as South Korea (6.8%) and Japan (6.6%) among adults aged 20 to 79. Type 2 diabetes mellitus (T2DM) is known to be strongly influenced by genetic factors, and in recent years, significant research has focused on identifying associated genetic variants. Among the numerous genes linked to T2DM, the TCF7L2 gene has been extensively studied. TCF7L2 (Transcription Factor 7-Like 2) is located on the short arm of chromosome 10 at locus q25.2 25.3. It consists of 19 exons and encodes a protein comprising 619 amino acids. As a transcription factor, TCF7L2 plays a critical regulatory role in various processes, including pancreatic β-cell function, insulin secretion, insulin receptor activity, and multiple intracellular biochemical signaling pathways. Objectives of the study: Genomic DNA was extracted from the blood samples of individuals diagnosed with type 2 diabetes mellitus (ICD-10 code: E11), and a specific region of the TCF7L2 gene was amplified and detected using PCR. Reasearch materials and methods: This study employed an experimental research design and used purposive sampling to recruit 30 participants who had been diagnosed with type 2 diabetes mellitus (ICD-10: E11). A total of 5–10 mL of peripheral blood was collected from each participant in EDTA-containing tubes. Genomic DNA (gDNA) was extracted from 30 samples, and the DNA yield was quantified using a NanoDrop spectrophotometer. The extracted gDNA was then used as a template for the amplification of an 888 base pair (bp) fragment of the TCF7L2 gene using polymerase chain reaction (PCR). The PCR products were verified by gel electrophoresis, confirming the presence of the expected 888 bp amplicon. Conclusion Blood samples from 30 individuals diagnosed with type 2 diabetes mellitus (T2DM) were analyzed. The extracted DNA showed a purity range of 1.73 to 2.1 (A260/A280), indicating that the samples met the general quality requirements for PCR. DNA concentrations measured using a NanoDrop spectrophotometer ranged from 12.7 to 54.3 ng/µl, which is sufficient for downstream PCR analysis. The TCF7L2 gene, known to be associated with the development of T2DM, was detected in 26% of the total samples.