Multidrug resistance (MDR) to chemotherapeutic drugs has been shown to be mediated by overexpression of the energy dependent efflux pumps like P-glycoprotein (P-gp), which reduce the intracellular drug concentration below cytotoxic levels. The search for MDR reverters is an important task for improving anti-cancer chemotherapy. The objective of this study was to investigate the multidrug resistance reversal effect of Chinese herbal extracts used in clinical practice. The effects of various Chinese plant extracts were studied on modulation of P-glycoprotein using Rhodamine 123 accumulation assay on mouse lymphoma cell line transfected with human mdr1 gene and on human breast cancer KCR/MDR cell line. Some of the most effective compounds were assayed for their antiproliferative effects in combination with anticancer drug in checkerboard microplate method and found to have synergisms.