Objective:To investigate the inhibitory effects of paclitaxel alone or combined with cisplatin against human breast cancer line MCF-7 in vitro,and to explore the related mechanisms with MAPK pathway and Bcl-2 gene family. Methods: MCF-7 cells were treated by paclitaxel with or without cisplatin,and the proliferation and 50% inhibitory concentration (IC50) were calculated by cell counting kit-8 assay. The effects of ERK pathway inhibitor (U0126) and JNK pathway inhibitor (sp600125) on cell proliferation were also observed. Flow cytometry was used to determine cell cycle distribution,and Western blot was used to detect the protein expression level changes of MAPK pathway members,Bcl-2 and Bax when cells were given different treatments. Results: Paclitaxel(0.025~0.400 μmol/L) combined with cisplatin(1~16 μmol/L) showed an obvious synergistic effect(CI < 0.95). Sp600125 could significantly inhibit MCF-7 growth in vitro. Sp600125 combined with paclitaxel or cisplatin had a better antitumor activity than paclitaxel or cisplatin used alone. When treated with paclitaxel and cisplatin together,the cells at G2/M phase were less than paclitaxel group but more than cisplatin group. Combination of paclitaxel and cisplatin was found to decrease p-ERK,Bcl-2 protein levels in contrast with paclitaxel group or cisplatin group and increase p-JNK/p-SAPK,p-p38 protein levels in contrast with control group after 48 hours. Conclusion: Combination of paclitaxel and cisplatin in vitro showed synergistic effect. JNK pathway inhibitor combined with paclitaxel and cisplatin showed more powerful inhibition on MCF-7 cells than the two drug combination. Combination of paclitaxel and cisplatin seems to limit the accumulation of MCF-7 cells in G2/M and activate JNK and p38 signal pathway while inhibit the activation of ERK signal pathway.