Functional foods are groups of foods that have potentially positive effects on health beyond basic nutrition. Probiotics are beneficial microorganisms, being as a group of functional foods, and when ingested in adequate amounts, they possess positive health effects to host organisms including having anti-carcinogenic functions, yet their exact mechanisms how they possess anti-carcinogenic activities are still under investigation. Another group of functional foods is plant-based phenolic compounds. They also have potential to possess anti-carcinogenic activities. Among them, oleuropein is very interesting and well-known phenolic compound naturally present in olive fruits and olive oil. As the phenolic compounds and probiotic bacteria can be present at the same time in human gastrointestinal tract, this study aims to investigate the in vitro cytotoxic effects of Lactobacillus acidophilus LA-5 (LA5) and Lactobacillus rhamnosus GG (GG) grown in the presence of oleuropein on human prostate cancer cell line. For this, oleuropein was added to media of these bacteria and effects of cell-free supernatants of these combinations (phenolic+probiotic) on cytotoxicity of prostate cancer cell line PC-3 were investigated using MTT Method. Different concentrations of oleuropein were added to bacterial cultures and oleuropein added to the growth medium of LA-5 had additional effects on the cytotoxicity of cell-free supernatants of this bacterium. However, addition of oleuropein to the growth medium of GG did not show significant changes on the cytotoxicity of cell-free supernatants of this bacterium. Thus, the results indicate that new combinations of functional foods have potential to formulate new nutraceuticals.