The effect of lactic acid bacterial fermentation on sugars, organic acids, bio-transformation of phenolic compounds (anthocyanins and ellagic acid), and antioxidant activity was investigated in pomegranate juice. L. plantarum and L. acidophilus were used as probiotic starter organisms. Both bacteria were able to grow in the juice and their viable cells reached to 3.9×10⁸ CFU/mL after 72 h of fermentation. Fructose and glucose of the juice were significantly consumed by both probiotic starter cultures, and L. plantarum utilized more sugars in comparison with L. acidophilus. Glucose degradation rate was higher than fructose. The concentration of citric acid, as the main acid found in the juice, was significantly reduced by both bacteria through the first 48 h of the process (P < 0.05). Lactic acid was detected as the most abundant acidic metabolite (6.1 g/L) produced within the fermentation, especially by L. plantarum. LC/MS analysis of different anthocyanins, revealed that these compounds (except pelargonidin 3-glucoside) were significantly decreased in the pomegranate juice after fermentation. DPPH Radical scavenging studies showed that fermentation of pomegranate juice using selected probiotic starters increased the antioxidant activity significantly (P < 0.05). In addition, L. acidophilus improved the antioxidant activity of the juice more extensively than L. plantarum. The results of this study showed that fermentation of pomegranate juice by probiotic bacteria would enhance the health benefits of the juice.