Abstract: 【Objective】To study the appearance, distribution and quantity variation of immunocytes—T lymphocytes and its subpopulations and B lymphocytes in different periods, analyzing the developmental process of immunocytes in the chicken crop.【Method】The mono-antibodies and immunohistochemistry was used to observe the distribution and count the number of the relevant cell in every age. 【Result and conclusion】The results showed that CD3⁺, CD4⁺ and CD8⁺ cells appeared in the first day after post-hatching. Bu-1b⁺ cells were observed in the 4rh day. CD3⁺ cells mainly distributed in the epithelium and lamina propria, and the lymphoid aggregates covered by CD3⁺ cells were first observed in the 7th day after post-hatching. CD4⁺ cells were located in the lamina propria. At first, CD8⁺ cells mainly distributed in the lamina propria of the mucosa. With the age increasing, CD8⁺ cells slightly migrated and infiltrated to the epithelium of the mucosa，which were transformed to the lymphoepithelium. Bu-1b⁺ cells mainly distributed in the lamina propria, especially around the vessels. The germinal center which was covered by the Bu-1a⁺ cells was first observed in the 35th day after post-hatching. The amount of CD3⁺, CD4⁺, and CD8⁺ cells kept increasing with the age; the amount of parts of positive cells decreased in the 14th and 21th day; it slightly increased after this date and reached mature level around the 56th day. Bu-1b⁺ cells continuously kept increasing with age, its rising rate was higher than T lymphocytes during the later period. The research showed that as a part of the digest system in the chicken, the crop posses ses the mucosal immunity which consists of the lymphoid aggregates and the lymphocytes.The crop is an important part of gut-associated lymphoid tissue(GALT).