Background: Obesity is linked to metabolic disorders that result in tissue damage and malfunction. In addition to impairing immunity, obesity is associated with low-grade chronic inflammation. Objective: The aim of the current study is to assess the effect of treadmill training on immunoglobulin G and C-reactive protein (CRP), body mass index (BMI) and waist circumference (WC) in obese adolescents' girls. Patients and methods: A total of 60 obese adolescent girls were selected from National Nutrition Institute aged from 12 to 18 years old. All girls were randomly assigned into two groups. Control group included 30 girls who received diet control therapy only. Study group included 30 girls who received treadmill gait training (3 sessions/per week) in addition to diet control therapy. All girls in both groups were assessed before and after three successive months as Immunoglobulin G and CRP were measured using blood analysis, BMI calculated by weight in kilograms (Kg) divided by the girls' height in meter squared (m²) while waist circumference by Graduated measuring tape. Results: There was a statistically significant increase in IgG level, and a statistically significant decrease in CRP, BMI and WC in both groups; these changes were more in the study than the control, but there was no statistically significant difference in IgG, CRP, BMI and WC when comparing post-treatment results of both groups. Conclusion: Treadmill gait training is an effective modality that can be used in the rehabilitation program in obese adolescents for improving their immune functions and reducing inflammatory reactions.