Abstract: This study was undertaken to determine the suitability of different doses (0, 0.5, 1.0 and 1.5%) of Denak powder (Oliveria decumbens Vent) on viability of Lactobacillus acidophilus and Bifidobacterium bifidum in milk and yoghurt during 21 day refrigerated storage for production of probiotic herbal milk and yoghurt. In order to determine the effect of different doses of Denak powder on growth of probiotic bacteria in milk and yoghurt, first lyophilized bacteria Lactobacillus acidophilus was added to 1 liter of low fat sterilized milk and was considered as control. Denak powder at the concentrations of 0.5, 1 and 1.5% were added to the samples and incubated until acidity reached 40° Dornic and then left in refrigerator. Similar procedure was applied to the bacteria Bifidobacterium bifidum. The results of this experiment indicate the positive correlation between increased bacterial growth and increased Denak concentration. The investigation showed that the yoghurt containing 1% Denak powder had the best for taste, color, and insolubility. The sample with 1.5% Denak powder in milk and yoghurt had greater viscosity than the other samples investigated. The shelf lives of products were determined to be 21 days during which the bacterial count decreased but not less than 109. All the results suggest that Denak (Oliveria decumbens Vent) promoted the metabolism of lactic acid bacteria in milk and yoghurt. According to these findings, addition of Denak powder to milk and yoghurt can be recommended to take advantage of their beneficial properties on human health attributed to antimicrobial activities.