There was researched the effect of the kvatronan-Se preparation and two complexes of nanocarboxylates on the reproductive function of cows, in particular their fertility, biochemical and hormonal status. For experimental research, there were formed four groups of cows – the control group included intact animals and three experimental ones. The cows of the 1st experimental group were subcutancously injected with a complex of nanocarboxylates Se, Cu, Mn, Cr; of the 2nd group – with kvatronan-Se preparation; of the 3rd – with Ge, Cu, Mn, Cr. . It has been found that kvatronan-Se injections (2nd experimental group) on the 10-12th day of the sexual cycle increases the fertility of cows by 27.3; (compared with the control); by 18.2 and 9.0%, respectively, compared to the 1st (complex of Se, Cu, Mn, Cr) and 2nd experimental group (Ge, Cu, Mn, Cr). It should be noted that the specified preparation and complexes of nanocarboxylates with microelements stimulate metabolic processes in the body of animals. For example, on the 13th day of sexual cycle the glucose content increased in experimental groups: in the 1st group by 7.6; 2nd – 14.2; 3rd – 4.5%; the leved inereased cholesterol by 15.2; 15.6; 14.5 %, respectively. Concentration of total protein in the second group increased by 30.75, in the 3rd group – 2.60 %. In the group 1st they observed the tendency to a decrease by 2.1%. It has been established that kvatronan-Se preparation and the complex of Ge, Cu, Mn, Cr promote the synthesis of sex hormones, such as progesterone, which level in these groups increased by 20.3 and 16.9 % on the 13th day of the sexual cycle. Dynamics of estradiol and testosterone concentration in all experimental groups did not change significantly. Therefore, kvatronan-Se is the most effective preparation in stimulating the reproductive function of cows, and changes that occur in the body of animals are considered to be favorable for implantation of the embryo. Key words: .