The work aims at studying the bone tissue mineral density in children born with low body weight, taking into account the dependence on the nature of feeding and polymorphism of the C/A gene polymorphism of COL1A1_1 collagen gene (rs1107946). Materials and methods. The study involved 74 children. Of these, 29 children born with the body weight of 1500-1999 g were in the observation group I; 25 children weighing 2000-2499 g-group II; 20 children with the body weight at birth of 2500 g-group III (control group). All children were under inpatient treatment at the Municipal Non-Profit Enterprise "City Children Hospital no. 5" of Zaporizhia City Council. Data on the type of breastfeeding of a child aged under 1 year were analyzed for all children. The study of bone