Doogh is a traditional Iranian drink prepared by fragmentation and dilution of yogurt, with addition of salt and flavouring. Dairy products are favorable environment for microbial growth due to high nutrient and relative humidity. One of the most important parameters in the food industry production and consumption is enhancing the shelf life of the product. Therefore, food additives such as potassium sorbate are used in this regard. While application of potassium sorbate as a preservative with excellent antibacterial and antifungal properties in various foods is common, but its addition into Doogh is forbidden according to national standards of Iran. The objective of this study was to determine the prevalence of preservatives in Doogh in West Azerbaijan province, Iran, from 2011 to 2014. 172 samples of various commercial Doogh were tested for determination of potassium sorbate. The results showed that 14.6% of samples were contaminated with preservatives and the highest and average concentration of this preservative in analyzed samples was 722.4 and 27.136 mg/kg respectively during the past 3 years.