Abstract: OBJECTIVE To study the regulating effect of interleukin-12（IL-12） monoclonal antibody on the helper T cell 1/helper T cell 2（Th1/Th2） immune balance in Crohn’s disease model mice. METHODS Totally 30 healthy BALB/c mice were selected and divided into 10 of the normal control group（10 mice） and the 20 of experimental group. The experimental group were treated with crohn’s disease model. After successful modeling, The experimental group with successful modeling were divided into 10 of the crohn’s disease group and 10 of the IL-12 monoclonal antibody group（10 mice each）. The IL-12 mAb treatment group were received intraperitoneal injection of IL-12 mAb（25 mg/kg, once per week）, and the control group and Crohn disease group were given intraperitoneal injection of 0.2 mL of normal saline. After 4 weeks of treatment, the degree of disease activity, colon weight and colon length of three groups of mice were evaluated. The levels of Th1 cytokine such as interferon-γ（IFN-γ）, tumor necrosis factor-α（TNF-α）, interleukin-1β（IL-1β）, interleukin-8（IL-8）, and Th2 cytokines including IL-4, IL-10, IL-12 and IL-23 in the colon tissue of three groups of mice were detected by enzyme-linked immunosorbent assay. RESULTS The scores of disease activity, Th1 cytokines including IFN-γ, TNF-α, IL-1β, IL-8, IL-12 and IL-23 in Crohn’s disease group were（4.12±0.23）,（563.49±21.36）ng/ml,（120.69±6.69） ng/L,（43.73±3.58） ng/ml,（179.68±4.26）ng/ml,（148.69±6.58） ng/L and（762.58±26.58） pg/ml, respectively, significantly higher than those in the monoclonal antibody group（1.62±0.17） points,（472.59±15.64）ng/ml,（106.25±3.27）ng/L,（37.62±2.16）ng/ml,（163.57±3.12）ng/ml,（98.67±5.12）ng/L, and（412.68±16.98）pg/ml, respectively and the control group, while the colon weight/length was（42.36±3.16）mg/cm, significantly greater than that of the IL-12 monoclone antibody group（33.59±2.07）mg/cm and the control group mice. The Th2 type cytokines IL-2 in the colon tissue including IL-4 and IL-10 were（55.27±1.62）pg/ml and（90.27±3.68） pg/ml, respectively, significantly lower than that of IL-12 monoclonal antibody group（61.27±2.21）pg/ml and（98.67±1.68）pg/ml, respectively and control group（P＜0.05）. CONCLUSION IL-12 monoclonal antibody could regulate the immune balance of Th1/Th2 by improving the abnormal expression of Th1 and Th2 cytokines, and then suppressed the inflammatory response of Crohn’s disease and had a therapeutic effect.