---

Background and purpose: Royal jelly (RJ) is a substance synthesized by worker bee- is shown to have various biological activities on different cells and tissues of the human body. In this study the effect of RJ on peripheral blood mononuclear cells cytotoxicity against the K562 Erythroleukemia cell line was investigated. Material and methods: In this experimental study human PBMCs (106 cells/ml) were separately cultured in standard conditions. The cells were then incubated with different concentrations of RJ (5 mg/ml, 10 mg/ml, 25 mg/ml) for 72 hours. Subsequently, cytotoxic effect of PBMCs pulsed with RJ on K562 was evaluated by Anexin PI test (Flow cytometry). Results: In the Anexin PI test, apoptotic property and cytotoxic effect of PBMCs pulsed with RJ on K562 increased significantly compared to those of the control group. Conclusion: PBMCs pulsed with RJ increased survival rate of PBMCs after treatment with RJ. This compound could be beneficial in preventing and controlling carcinoma cells.