Abstract: Objective :To examine the expression of the cyclin- dependent kinase inhibitor p27and P-glycoprotein (P-gp) in multicellular spheroids (MCS) of ovarian cancer and to determine a po-tential method for reversing P-gp-mediated multidrug resistance. Methods :A2780 and CAOV3 multi-cellular spheroids of ovarian cancer were obtained from three-dimensional culture and were used asmodels in this experiment. Both anti-sense (ASON) and sense- oligodeoxynucleotide (SON) were trans-duced into A2780 and CAOV3 cell lines by liposome. The expression of p27 and P-gp was detectedusing Western blot and flow cytometry (FACS), and the sub-cellular distribution of p27 and P- gp wasdetected by laser confocal microscopy. Results : Compared with monolayer cells, the expression of bothp27 and P-gp in MCS cells was significantly elevated. Low expression of P-gp was detected in mono-layer cells, but the expression of P-gp in cell aggregates was significantly elevated. The p27-ASON-mediated down- regulation of p27 decreased the level of P-gp protein. Conclusions :High expression ofP-gp in ovarian cancer multi- cellular spheroids may be consistent with an increased level of p27. Thep27-ASON may down- regulate the expression of P-gp, an effect that may be useful for reversing P-gp-mediated multidrug resistance.