Objective: To investigate the reversal effects of MDR1 gene on multidrug resistance in the glioblastoma cell line BT325 by magnetic chitosan-Fe3O4 nanoparticle-encapsulated MDR1 siRNA. Methods: The shRNA expression vector was constructed and the recombinant plasmids were cloned. Magnetic chitosan-Fe3O4 nanoparticles were prepared and the encapsulation rate was determined. After transfection, the BT325 cells were cultured to assay the transfection efficiency. The changing of MDR1 mRNA level and P-gp protein was evaluated. And the sensitivity to different chemotherapeutic drugs was assessed in BT325-siRNA transfected cell and untransfected cell by IC50 values. Results: The MDR1 RNAi plasmid was successfully designed and preparation. The encapsulation efficiency of the magnetic chitosan-Fe3O4 nanoparticle was 98-99%. The transfection efficiency of the siRNA-nanoparticles in BT325 cells was 70-80%. And the MDR1 mRNA levels were downregulated by reverse transcription (RT)-PCR assay. Furthermore, the results of P-gp protein expression decreased on immunocytochemical assay, Western blot and flow cytometry compared with control group. The IC50 values of DOX and VCR were decreased between the transfected cell and normal BT325 cell. Conclusion: After targeted transfection of the glioblastoma cell line with magnetic chitosan-Fe3O4 nanoparticle-encapsulated MDR1 siRNA, the expression of MDR1 at both the mRNA and protein level decreased, which increased sensitivity to chemotherapy in vitro. It might provide a basis for investigation of the mechanism involved in multidrug resistance in glioma.