Yoghurt samples treated with Teucrium polium essential oil (EO; 40, 60 and 80 ppm) and Lactobacillus casei (10 8 –10 9 cfu/mL) were stored up to 28 days at 4C. The physicochemical, viability of L. casei and organoleptic properties of yoghurt samples were analyzed at a 7-day interval during storage. A gradual increase in acidity was observed, whereas a decline in pH and solid nonfat contents was noted in all the samples (P < 0.05). Changes in protein and fat content of yoghurt samples during storage period were not remarkable. The survival of L. casei decreased throughout the storage period. Nevertheless, probiotic yoghurt and treatment containing 60 ppm EO had the highest (P < 0.05) viable count of probiotic bacteria (6.44cfu/g). Considering the organoleptic effect of the EO, the best treatment with acceptable flavor, good appearance without any signs of spoilage organisms and also with appropriated viability of L. casei was obtained at combination of 40 ppm EO and probiotic. PRACTICAL APPLICATIONS Based on our results, yoghurt can be a very suitable food product to carry relevant probiotic bacteria while adding certain herbal EOs. In this study, T. polium EO had adverse effect neither on physicochemical properties nor on the viability of L. casei of yoghurt. In addition, T. polium EO is nontoxic and safe for public health, so it can be an acceptable alternative to chemical preservatives.