Abstract: 【Objective】 The immunohistochemical localization and developmental changes of ghrelin in the duck thymus were studied to provide the morphological effect of ghrelin on the physiological function of thymus. 【Method】 Tianfu ducks were divided into 19 groups as follows: 7 groups in the embryonic period (14, 16, 18, 20, 22, 24 and 26 days at embryonic stage), 12 groups after hatching (at neonatal stage, 1, 3, 5, 8, 11, 14, 17, 20, 26, 29 and 32 weeks). The immunohistochemical method associated with morphometric analysis was used. 【Result and conclusion】 The ghrelin immunoreactivity (-ir) cells with round, ovoid, stellate and irregular aspects were maily thymic epitheilial cells and macrophages, and diffusely distributed in the thymic cortex and medulla from embryonic 20 days to 32 weeks after hatching. The number of ghrelin-ir cells in the thymic cortex and medulla was unchanged during the embryonic development, presenting a wave-changed pattern during the continuous development (from neonatal stage to 8 weeks after hatching) and matured periods (from 11 to 17 weeks after hatching ), which decreased during the involution stage (from 20 to 32 weeks after hatching). These results suggested that ghrelin-ir cells existed in the duck thymus and their numbers exhibited obvious age-related changes, which can be closely related to the involution of the duck thymus.