Objective：To investigate the effects of tripartite motif containing 25（TRIM25） overexpression on the chemotherapeutic drug sensitivity of human lung cancer cell line H1299 to cisplatin and the molecular mechanisms. Methods：TRIM25 overexpression plas－mid vector was constructed by gene cloning techniques and was transfected into H1299 cells. Efficiency of transfecion was observed under fluorescence microscope. Western blot was used to determine the TRIM25 protein expression level and the change of pyruvate ki－nase isozyme type M2（PKM2） protein level when TRIM25 was overexpressed. After treating untransfected and transfected H1299 cells with cisplatin for 24 h，drug resistance was detected by MTT assay and apoptosis was detected by Annexin V/PI. Results：Compared with those of H1299 blank group and pGCMV/neo empty carrier group，TRIM25 protein levels of pGCMV-trim25 transfection group were significantly increased（P=0.003，P=0.005 respectively）. Moreover，when up-regulating the TRIM25，PKM2 expression was reduced（P=0.001，P=0.003 respectively）. After cisplatin treatment，drug sensitivity as well as apoptosis rate of pGCMV-trim25 trans－fection group were significantly decreased（P<0.001，P<0.001）. Conclusions：Overexpression of TRIM25 protein in lung cancer cells H1299 could decrease the drug sensitivity to cisplatin by down-regulating expressions of PKM2.