Background: on-line hemodiafiltration (HDF) is a technique of renal replacement therapy which combines diffusion with convection and uses ultrapure dialysate as a replacement fluid, this technique allowing removal of middle molecular weight uremic toxins. Aim: To compare the effect of on-line hemodiafiltration versus conventional HD regarding the control of renal osteodystrophy. Methods: This study included 16 pediatric patients with age range 4-16 with ESRD on maintenance hemodialysis, they were converted to on-line HDF for three months. Clinical, laboratory and radiological manifestations of ROD were compared for both modalities. Results: The mean level of serum P decreased from 4.9mg/dl to 4.2mg/dl (p=.04), the mean level of PTH decreased from 749pg/ml to 404pg/ml (p=0.001), with significant improvement in bony pains (p=.029) and no change in the X-ray findings. Conclusion: On-line HDF improves the control of ROD in children with ESRD.