In this scientific paper are revealed the investigations regarding some immunological aspects, characteristic to the cellular immunity at the new born calves at different age periods. The purpose of the research consists of studying the cellular immunity activity at the neonatal calves, expressed by determination of the immunocompetent cells indexes, determination of the phagocytic activity and intensity. The researches reveal the importance of the cellular immunity, highlighting the aspects of immunocompetent cells and phagocytic mechanisms – which represent important indicators of the animal immune status. Due to the aforementioned, the dynamics of T and B lymphocytes in different age periods revealed important values in comparative aspect. The level of T and B lymphocytes constituted 14,4 ± 0,075 and 5,85 ± 0,008 at the age of 5 days, compared to the age of 10 days where these indexes constituted13,4 ± 0,008 and 10,0±0,81. Simultaneously at the age of 20 and 30 days the T and B lymphocytes values determined characteristic important values, which constituted 16,0 ± 0,08 and 12,0 ± 0,81, compared to 14,2 ± 0,08 and 12,28 ± 0,008 The dynamics of the phagocytic activity indexes demonstates that in the neonatal period at the calves aged of 5 days the phagocytic activity constituted 52,33 ± 0,60, compared to those aged of 10 days, which constituted 41,67 ± 0,65, fact which reveals a decrease expressed by different aspects of the external factors, acting on the newborn animal in the first days of life. Analysing the dynamics of the phagocytic activity indexes at the age of 20 and 30 days was stated, that the values constituted 38,56 ± 0,56 and 35,44 ± 0,47, fact which confirms the decreasing of the phagocytic processes at these animals. Relevant data were registered, regarding the phagocytic intensity of the neonatal animals at the age of 5 and 10 days, which constituted 2,32 ± 0,02 şi 1,83 ± 0,01, compared with the animals at the age of 20 and 30 days , where these values constituted 1.78 ± 0.01 and 1.57 ± 0.01. The results of the scientific research, regarding the activity of the cellular immunity at the neonatl calves, confirms the fact that the defense mechanisms are not enough triggered to protect the microorganisms against the viruses and other pathogenic agents. Therefore, the evaluation of the formation mechanisms of the immune system at the new born animal offers the possibility to wath the evolution of the cellular and humoral reactions, which mentains immune the homeostasis of the organism, of the defense cellular and humoral factors considered the most important in regulation of the immune system.