Background: Phosphate is an essential biologic element; phosphate is required by all cells for normal function and is a critical component of all living organisms. In patient with chronic kidney disease (CKD) stages 2 and 3, the ability to excrete phosphate load is diminished.this work was aiming to detect the early changes occurring in CKD-MBD regarding the urinary phosphorous excretion This is a case-control study applied on 100 subjects admitted to Benha university hospital and Kafr shokr hospital during the period from October 2017 to December 2018.The one hundred subjects were classified into four groups: The first group included twenty five patients with stage 1 CKD The second group included twenty five patients with stage 2 CKD The third group included twenty five patients with stage 3a CKD The fourth group included twenty five apparently healthy subjects serving as control. Serum phosphorous was 3.39+ .52 in stage1CKD, 3.45+.50 in stage2CKD, and 3.845 + .51 in stage3CKD and 24h urinary phosphorous excretion was 714.415+ 171.49 in stage1CKD, 587.035+126.23 in stage2CKD and 429.435 +141 .53 in stage3CKD. 24h urinary phosphorous excretion might be used to identify which patient with early stage of CKD with normal serum phosphorous level might benefit from oral phosphate binder and cardiovascular intervention in patient with CKD