BACKGROUND: The extensive consumption of milk anddairy products makes these foodstuffs targets for potentialadulteration with financial gains for unscrupulous producers.OBJECTIVES: The aim of this study was using PCR assay todetect cow milk in labeled sheep milk, sheep yoghurt, andLighvan cheese (a traditional ripened cheese produced fromsheep's milk). METHODS: The assay utilized primers targetingthe mitochondrial 12s and 16s rRNA gene. In this study, 35samples of sheep milk, 35 samples of sheep yoghurt, and 35samples of Lighvan cheese were purchased from differentsupermarkets in Mashhad city with different batch numbers.RESULTS: The results showed only 21 out of 105 (20%) samplescontained pure sheep milk. Undeclared presence of cow and goatmilk was detected in 33(31.5%) and 68(65%) of the 105 samples,respectively. CONCLUSIONS: It seems the PCR based analyticalmethod is an applicable technique to monitor adulteration indairy products.