Multidrug resistance (MDR) of cancer cells is, at least in part, associated with the overexpression of P-glycoprotein (P-gp). Many studies have demonstrated that natural compounds obtained from fruits, vegetables, teas and medicinal plants may modulate P-gp activity. The objective of the present investigation was to examine the effect of seven natural compounds on the P-gp activity in human uterine sarcoma cell line, MES-SA/DX5. Daunomycin uptake was significantly increased by biochanin A and silymarin (p<0.0001) whereas it was reduced by morin (p<0.01). The efflux of daunomycin from the cells was significantly inhibited by biochanin A, morin, cephalotaxine, berberine (p<0.05) and silymarin (p<0.0001). Biochanin A, berberine and silymarin significantly decreased $IC_{50}$ value of daunomycin (p<0.05) while morin increased it (p<0.05). These results suggest that some natural compounds such as biochanin A and silymarin may inhibit P-gp function and can be developed as MDR reversing agents to improve the efficacy of chemotherapeutic drugs when administered concomitantly.