Abstract: To investigate the multi-drug resistance reversal effect of IL-2 using monoclonal antibodies against breast cancer on the human breast cancer cell line MCF-7/ADM and to evaluate the feasibility of the method as an anti-tumor treatment. Methods: Recombinant human interleukin-2 and monoclonal antibodies against human breast cancer were prepared. The antibodies and cytokine were coupled, and the product, designated as Ab-IL2, was purified and its ability to reverse clinical multidrug resistance ( MDR ) was verified. Meanwhile, the retention of Ab-IL2 was measured through an in vivo MDR reversal trial. Adriamycin ( ADM )-resistant human breast cancer MCF-7 ( MCF-7/ADM ) cells were subcutaneously injected into female BALB/c nude mice at 106 cells per mouse. These mice were then divided into three groups: a. Control group, injected with normal saline; b. ADM group, injected with ADM at 1 mg/kg body weight; c. Collaborative treatment group, treated with both ADM at 1 mg/kg body weight and Ab-IL2 at 1 mg/kg body weight. The injections were given on the 14th and 19th day after inoculation. The diameter of the tumors were measured on the 14th, 16th, 18th and 20th day, and the volumes of the tumors were calculated according to the formula V = 0.5ab2. The mice were sacrificed after the last measurement, the tumor masses were surgically isolated and weighted, and the values were used to calculate the inhibition rate. Results: Ab-IL2 has a retention rate of 90.7%. Ab-IL2 showed strong synergistic antitumor effect with ADM in vivo, as suggested by the 3.11-fold higher tumor inhibition rate of the collaborative treatment group ( 60.48% ) compared with that of the ADM group ( 19.44% ) based on the data collected on the 20th day. Conclusion: Monoclonal antibodies can increase the specificity of the reversal agent, which could be helpful in reversing MDR. This study provides a safe and effective method for reversing multidrug resistance in tumors.