Background: Beta-thalassemia major (B-TM) is a genetic disorder characterized by impaired hemoglobin synthesis, leading to hemolytic anemia and associated complications. This study aimed to assess the diagnostic value of serum Osteoprotegerin (OPG) as an early biomarker for osteoporosis in B-TM children. Patients and Methods: A cross-sectional study was conducted at the Pediatric Department of Benha University Hospital from January 2022 to December 2022. The study included 64 children aged 2 to 18 years, divided into two groups: Group 1 consisted of 40 children with β-thalassemia (cases group), and Group 2 consisted of 24 age and sex-matched healthy children (control group). Various parameters including Hb, OPG, vitamin D3, and ferritin were measured using enzyme-linked immune sorbent assay. Result: The study also examined the relationship between these biomarkers, Body Mass Index (BMI), and splenic status. The results showed significantly decreased levels of Hb, and vitamin D3 in β-thalassemic patients compared to the healthy group (P