Background: Studies have shown that using hypotonic fluids may result in hyponatremia and the use of isotonic fluids is associated with lower incidence of electrolyte disturbances. Renal functions usually based on measurements of serum urea and creatinine are dependent on the maintenance of appropriate intravascular volume in order to maintain adequate organ perfusion and functioning. Aims and Objectives: To analyze the short term effect of IV Fluids in PICU on serum electrolytes and renal function tests. Methods: This observational descriptive study was conducted in 125 children admitted PICU from April 2022 to September 2022 receiving IV fluids and kept nil by mouth. The levels of serum sodium, potassium, urea and creatinine done at day1 of admission were compared to the investigations done after 72hrs.The data was categorized based on the type of fluid received by the child. Hypotonic fluids (0.45% DNS, D10) and isotonic fluids (0.9% DNS). Results: Out of 125 children, 61(48.8%) received hypotonic fluids whereas 64(51.2%) received isotonic fluids. The average volume of hypotonic fluid given was 3.2±1.7 ml/kg/hr whereas of isotonic fluid given was 2.7±1.3 ml/kg/hr (p=0.11). Hyponatremia developed in 16 out of 42 baseline normal sodium patients in hypotonic group and 6 out of 46 in isotonic group(p=0.03). Serum creatinine was raised in 6(12%) patients out of 50 baseline normal patients in hypotonic group. Serum urea from baseline normal was raised in 7(21.9%) in hypotonic and in 5(17.9%) in isotonic group (p=0.4). Mortality was significantly higher in hypotonic group (13.1%) compared to isotonic group (3.1%) (p=0.04). Conclusions:For preventing positive fluid balance and also development of hyponatremia, isotonic fluids should be considered as routine maintenance fluids.