Abstract: Objective To examine differential protein expression in drug-resistast human oral squamous carcinoma cell lines KBV200 before and after the treatment with five traditional Chinese medicines.Methods The cytotoxicity of traditional Chinese medicines to KBV200 cells were determined by methyl thiazol tetrazolium(MTT) assay.The different protein expression profiles in KBV200 cells were detected by surface enhanced laser desorption/ionization-time of flight-mass spectrometry(SELDI-TOF-MS) and CM -10 chip before and after the treatment with five traditional Chinese medicines at noncytotoxic dose combined with vincristine(VCR),respectively.Results At the range of 2 000-50 000 Da,13 differential protein expressions were identified before and after the treatment with epingallocatechian gallate(EGCG) in KBV200 cells (P<0.05).The five protein peaks(3 997,4 941,4 968,5 971,and 6 084 Da) were expressed at low level in KB cells but up-regulated obviously(P< 0.05) in KBV200 cells before the treatment with EGCG and dow n-regulated (P< 0.05) in KBV200 cells after the treatment with EGCG.Six differential protein expressions were identified in KBV200 cells (P<0.05) before and after the treatment with emodin,of which,three protein peaks(4 968,5 971,and 6 084 Da) were expressed at low level in KB cells but up-regulated obviously(P< 0.05) in KBV200 cells before the treatment and dow n-regulated (P< 0.05) in KBV200 cells after the treatment.No differential protein was simultaneously identified in KBV200 cells (P<0.05) before and after the treatment with nitidine and in KB cells.There also was no differential protein expression detected in KBV200 cells before and after treatment with Radix Isatidi extract or meadow rueleaf corydalis root extract.Conclusion Differentially expressed proteins can be captured before and after the treatment with EGCG and emodin and the proteins possiblly associate with reverse multidrug resistance of KBV200 cell lines in vitro.