Purpose: to study biochemical indicators of blood for prescribing and correct dosage of vitamin D in rickets. Materials and methods: 203 children under 1 year of age were under our observation. Serum 25(OH)D levels as well as calcium and phosphorus levels were determined in all children. Results: determination of the level of 25(OH)D3 in the blood serum of children with rickets showed a low level in 112 (86.1%) of those examined, and a normal level in 18 (13.8%). In 50 children (68.4%) with NTPZ, it was found that the level of 25 (OH) D was low, and in 23 (31.5%) this indicator was at a normal level. The average value of 25(OH)D3 in the blood serum of children with mild rickets was 15.23±1.32 nmol/l, and the average value was 18.75±2.76 nmol/l.Calcium and phosphorus levels in mild rickets are 2.13±0.03 and 0.96±0.02 mmol/l, respectively, in moderate rickets 1.73±0.02 and 0.77±0 It was .02 mmol/l. The amount of 25(OH)D3, calcium, and phosphorus in blood serum in children with rickets and NTPZ was 17.4±4.24 nmol/l, 1.96±0.05, and 0.88±0.03 mmol/l. Children had normal levels of Ca and P in the blood (2.48±0.07 and 1.11±0.40 mmol/l, respectively), so they received only vitamin D without taking additional calcium preparations. Conclusion: For children with rickets, the recommendation of vitamin D preparations in combination with calcium preparations and general strengthening treatment in the form of an individual scheme significantly increased the effectiveness of treatment. At the same time, there was a decrease in the clinical signs of rickets, its residual assorts, signs of spasmophilia, and an increase in the amount of 25 (OH) D3 in blood serum.