Vascularized ampullar dilatations of the cecal bases, called cecal tonsils, which are key components of avian gut-associated lymphoid tissues, are very strategic for the health of birds. The morphological development of the cecal tonsils of broiler chicken was evaluated using light microscopic and transmission electron microscopic techniques. A total of 10 fertile eggs and 50-day-old chicks of Marshall Broiler chicken were used for the study. On pre-hatch day (PrD) 19 and post-hatch day (PD) 1, the lamina epithelialis mucosae showed maturing enterocytes, goblet cells, and a basal lamina. Apicolateral tight junctions, adherent junctions, and desmosomes were frequently observed in the lamina epithelialis mucosae at PrD 19 and PDs 1, 35, and 56. However, at PDs 7, 14, and 21, the desmosomes were rarely observed. The lamina propria submucosae of the cecal tonsil showed areas of diffuse infiltration of lymphocytes on PDs 3 and 5, whereas areas of dense lymphocytic infiltration occurred on PDs 7, 11, 14, and 21. The population of plasma cells, which was first observed on PD 14, increased with age. In conclusion, the cecal tonsil of the broiler chicken assumes adult histological features through a gradual process that begins from PD 3 and continues until PD 35.