In this study, phenolic compounds and antioxidant activities in citrus fruits and their peels were determined, and their stimulatory roles on some lactic acid bacteria were investigated. Phenolic compounds in citrus fruits such as mandarin, lemon, orange and grapefruit were determined either in the juices or in the peel extracts. Total phenolic content was determined in a spectrophotometer at 685 nm using the adapted Folin-Ciocalteu method. Total flavonoid content was measured using LC/MS (liquid chromatography-mass spectrometry). The effects of the fruit juices and peel extracts on the selected lactic acid bacteria (Lactobacillus delbrueckii NRRL B5448, Lb. casei NRRL B1922, Lb. acidophilus NRRL B4495) were investigated. The tested lactic acid bacteria were significantly affected by chlorogenic acid, hesperidin, naringin and caffeic acid compared to the control samples (P?0.05). Antioxidant properties of fruit samples were also measured using the DPPH (2,2-diphenyl-1-picrylhydrazyl) method. The phenolics positively affected the metabolism of bacteria, with the stimulatory effects of the assayed samples being influenced by the phenolic profile.