Objective:The expression of mdr1 is associated with chemotherapeutic efficacy of cancer, some patientswith oral cancer are resistant to chemotherapy, the authors therefore investigated the mRNA expression level of mdr1 in oral squamous carcinoma. Methods:Totally 26 sampleswere investigated in this study, and the total RNAof oral squamous cell carcinoma each sample were extracted and hybridized with probe pchp-1 .The level of mdr1 were compared with the cell line Tca8113, Tca8113P100 and Tca8113P200, whichwere sensitive, resistant to VCR100 nmol and 200 nmol respectively.Results:The results showed that in the 26 patients, the mdr1 level ranged from0.3@105to 5@105. Among the 26 patients, 9 were drug-sensitive; 14 were lowdrug-re- sistant; and the other 3 were highly drug-resistant. The rate of drug resistance was 65%. The expression of mdr1 was not related with the pathologic differentiation and TNM classification.Conclusion:The multi-drug resistance of the malignant tumor to chemo- therapy is the important factor of unsatisfied effect of chemotherapy, and this paper systemically studied on the mdr1 expression of the oral squamous cell carcinoma, and the relation with pathologic differentiation and TNM classification. The result is important for choosing the chemotherapeutic regime for patients.