In poultry farms keep large poultry and demand permanently attention to their health. Seeing, the issue of conservation of livestock and prevention of bird disease will always be relevant. The task of conserving birds and increasing their productivity is inseperate linked to increasing natural resistance and the state of the immune system. An urgent problem in poultry farming is the choice of optimal vaccination programs for poultry. The study of the morphology of the immune system of birds allows to objectively assess the effectiveness of methods of prevention and treatment of diseases of various etiologies, as well as to identify critical periods of development of the immune system and the whole organism. Harderian gland is a peripheral organ of immune protection of birds, which is involved in the activation, differentiation of B-lymphocytes and proliferation of plasma cells. The purpose of the article is to systematize and describe the results of studies of the morphology of the ward gland of chickens for vaccine prophylaxis. It is established that the main morphological changes in the body during vaccine prophylaxis are: hyperplastic processes of lymphocytes and macrophages, as well as cellular transformation, which leads to the development of plasma cell response. As a result, there is an increase in the area of lymphoid tissue and an increase in the number of plasma cells in the ward gland. Morphofunctional changes in the harderian gland of chickens are due to age in the postnatal period of ontogenesis, and also depend on the frequency of vaccination. This review article is devoted to the study of the morphology of the harderian gland of chickens during vaccination. Data on the assessment of the morphofunctional state of the bird's harderian gland should be taken into account when conducting vaccine prophylaxis. In addition, a set of structural and morphometric changes in the harderian gland of chickens during vaccination may be one of the criteria for morphological diagnosis of avian immunodeficiencies.