Background/Aims: To study the effect of drugs on the expression of multidrug resistance gene in ulcerative. colitis. Methodology: The expressions of multidrug resistance (MDR) 1 gene and its product P-Gp were detected by reverse transcription-polymerase chain reaction and immunohistochemistry to realize the impact of drugs on ulcerative colitis. Results: MDR1 gene and P-Gp did not exhibit significant difference (P >0.05) before and after amino salicylic acid drug treatment. Compared with the control group, their expressions before treatment in the ineffective corticosteroid- and immunosuppressant-treated groups did not exhibit significant difference (P >0.05). Their pre- and post-treatment expressions in the ineffective groups were compared with those in the normal control group and in the effective group, and significant differences were observed (P <0.05). Conclusions: 5-Amino salicylic acid drugs have little effect on the expression of MDR1 and its product P-Gp. The expressions of MDR1 and P-Gp were much higher in groups that showed ineffectiveness for corticosteroids and immunosuppressants after treatment.