Purpose <p>Childhood obesity has become a significant global health concern. Socioeconomic status (SES) is a recognized determinant of obesity. This study aimed to examine the trends and socioeconomic inequality in the prevalence of obesity among Iranian children and adolescents from 2000 to 2016, and to project these trends to 2030.</p> Methods <p>This multi-center, serial cross-sectional study utilized data from five national surveys conducted in Iran between 2003 and 2016. Participants consisted of 76,957 children and adolescents (51% boys), aged 6 to 18 years. Principal component analysis (PCA) was used to categorize the socioeconomic status (SES) into three tertiles. The concentration index (CI) and slope index of inequality (SII) were employed to assess SES inequality across various obesity phenotypes, including general obesity (GO), abdominal obesity (AO), combined obesity (CO), isolated AO, and isolated GO.</p> Results <p>The prevalence of all obesity phenotypes increased between 2003 and 2016 and is projected to continue rising until 2030. Socioeconomic inequality, measured by CI and SII, initially favored higher SES groups but decreased over time, indicating a more even distribution of obesity across socioeconomic strata.</p> Conclusion <p>findings reveal a significant upward trend in the prevalence of obesity phenotypes from 2003 to 2016, with projections indicating this trend will continue through 2030.The disparity in obesity rates across SES groups is narrowing, indicating that obesity is becoming a widespread public health issue across all socioeconomic strata.</p> Clinical trial number <p>Not applicable.</p>