Introduction: Phototherapy is considered to be a risk factor for hypocalcemia and its mechanism is probably multifactorial.Objective: 1) To determine the effect of phototherapy on serum Calcium level in neonates receiving phototherapy. 2) To compare Serum Calcium level changes in preterm and term neonates.Study Design: present study is a prospective hospital based comparative study conducted over a period of 1yr.Result: The study included 100 neonates. The majority of study participants i.e, 75 were born at term whereas, 25 were born preterm. Among preterm infants, the mean serum calcium level before phototherapy was 8.96±0.62 mg/dl, which decreased to 8.39±0.76 mg/dl after phototherapy. Among term infants, the mean serum calcium level before phototherapy was 9.08±0.61 mg/dl, which decreased to 8.38±0.77 mg/dl after phototherapy.Conclusion: The present study suggested that phototherapy is associated with significant reductions in serum calcium particularly in term infants. Preterm infants also showed significant changes in serum calcium levels, emphasizing their vulnerability and the need for close monitoring.