Background: For the metabolism of bone minerals as well as the skeletal system's growth and development, vitamin D is essential. For all infants in their first year of life, In light of the prevalent problem of vitamin D insufficiency, esteemed health organizations such as the American Academy of Pediatrics (AAP) and the World Health Organization (WHO) advocate for the universal provision of 400 IU of oral vitamin D daily. Aim and Objectives: To determine the impact of regular vitamin D supplementation on the physical development of infants who are exclusively breastfed at the age of six months. Materials and methods: A randomised controlled trial was conducted at the Department of Paediatrics, after obtaining ethical clearance from the Institutional Ethical Clearance Committee. The study aimed to compare the growth parameters (weight, length, and head circumference) of exclusively breastfed, term, healthy infants supplemented with routine oral Vitamin D (400 IU daily) against those not supplemented.A total of 100 subjects were included in the study, with 50 infants in each group:Group I (Control Group): Exclusively breastfed, term, healthy infants who were not supplemented with routine oral Vitamin D.Group II (Supplemented Group): Exclusively breastfed, term, healthy infants who were supplemented with 400 IU of oral Vitamin D daily. Results: The comparison of growth parameters revealed that weight gain in Group I averaged 4.6 kg (±0.5), whereas in Group II, it averaged 4.9 kg (±0.6). The mean difference of 0.3 kg, with a 95% confidence interval (CI) of 0.2 to 0.5, was statistically significant (p-value <0.001). Length gain was 17.7 cm (±1.8) for Group I and 18.7 cm (±1.9) for Group II, with a mean difference of 1.0 cm and a 95% CI of 0.4 to 1.5, also statistically significant (p-value <0.001). Head circumference gain was 9.0 cm (±0.8) for Group I and 9.4 cm (±0.9) for Group II, with a mean difference of 0.4 cm and a 95% CI of 0.1 to 0.7, which was significant (p-value = 0.01).The incidence of rickets was observed in 3 infants from Group I and none from Group II. Hospitalization for more than three days was recorded for 5 infants in Group I and 2 infants in Group II, making a total of 7 cases. Other health issues were reported in 4 infants from Group I and 3 from Group II, resulting in a total of 7 cases. This indicates that vitamin D supplementation may reduce the incidence of rickets and other health complications. Conclusion: The study demonstrates that routine vitamin D supplementation in exclusively breastfed infants leads to significant improvements in physical growth parameters at six months of age. Supplemented infants showed greater weight gain, length gain, and head circumference gain, and had a lower incidence of rickets and hospitalizations compared to non-supplemented infants.