The article describes reactive changes in rats’ reproductive system as a result of potassium humate effect. The experiment involved 80 male and 32 female rats of one month of birth weighing 190–210 g. The animals were equally divided into 8 groups and received solution of potassium humate according to the group affiliation. Solution was preparedon distilled water and was administered to animals intragastrically on a daily basis in accordance with the group affiliation and timing at a dose of 10 mg / 100 g body weight, 1 ml. The control animals received 1 ml of distilled water. The animals were daily monitored. The following parameters were assessed depending on the duration of potassium humate intake: embryonic (pre- and post-implantation) mortality; backwardness in a form of decreased body weight and cranio-caudal sizes of fetuses. The experiment revealed that potassium humate administration before implantation and in the early stages of pregnancy causes increasing of corpora lutea and implantation sites number, so it increases insemination’s effectiveness, number of the pups in a litter, cranio-caudal sizes of fetuses, as well as average placenta weight and fetuses survival rate.