Background: Fibroblast Growth Factor 23 (FGF23) is considered as a marker of progression of kidney disease. Objective: the aim of the study: is to assess the effect of administration of calcium carbonate on serum FGF23 in normophosphatemic children with early stages CKD. Patients and Methods: Forty children with early CKD were enrolled in this case-control study. The patients were randomly divided equally into two groups A and B. Group A (received daily oral calcium-carbonate as a phosphate binder) over a period of 6 months, and group B (did not receive oral phosphate binder or calcimimetics). Baseline and follow up urea, creatinine, serum phosphate, serum calcium, alkaline phosphatase, 25 hydroxy vitamin D, parathormone (PTH) and serum FGF23 were obtained at the start and at the end of the study period. Results: Group A showed a significant decrease in serum levels of P, ALP and 25 hydroxy vitamin D (p-values: <0.001, 0.003, 0.0001 respectively). Also, there was non-significant decrease of PTH and serum FGF-23 (p-values: 0.39 and 0.396 respectively). While in group B there was a significant increase in levels of phosphate, PTH and FGF23 (p-values: 0.012, <0.001, <0.001) respectively, in contrast to significant decrease in levels of serum calcium and 25 hydroxy vitamin D (p-values: 0.033 and <0.001 respectively). Conclusion: Oral calcium-based phosphate binder has a role in decrease production of FGF23 and control secondary hyperparathyroidism in early CKD children.