Serum FGF23 is known to markedly rise in patients with chronic kidney disease and has been found to be associated with dysregulated mineral metabolism and cardiovascular morbidity and mortality in these patients. It was discovered also that FGF23 rise in patients with acute kidney injury and has been suggested that its high level in those patients is associated with adverse outcomes. Many different mechanisms have been suggested for the FGF23 rise in acute kidney injury which appears to be independent of its classic regulators as serum phosphate, PTH, and vitamin D. one of these possible mechanisms is decreased renal clearance of FGF23 with impaired renal function. In this study, correlation of FGF23 with serum creatinine and other laboratory markers were studied. Methods: This study was a cross-sectional study carried out at Mansoura university hospital. It included patients who were admitted to the nephrology unit with acute kidney injury. Those patients were subjected to taking history and careful examination and blood samples were taken at admission for basic laboratory investigations, serum creatinine, and serum FGF23 measurement. Results: The study included 64 patients. Serum FGF23 in those patients showed no correlation with serum creatinine at admission. However, it showed significant positive correlation with white blood cell count and platelet count. Conclusions: Serum FGF23 showed no correlation with serum creatinine at admission in patients with acute kidney injury.