The aim of this study was to determine the localization, distribution and heterogeneity of mast cells in the duodenum in prepubertal and postpubertal stage of partridges. For this purpose, tissue samples were taken from the duodenum of six prepubertal and six postpubertal stage of partridges. The tissue samples were fixed in 10% formol solution, processed by routine histological techniques, and embedded in paraffin. The tissue samples were stained with toluidine blue, alcian blue-safranin O and Crossman's triple staining methods. The presence of mast cells was detected in the head, middle and end of duodenum of the partridge. It was observed that the cells were mostly located in the tunica mucosa and tunica serosa of the duodenum, and very little in the muscular layer. It was determined that the number of mast cell was higher at prepubertal stage than at postpubertal stage (P<0.05). According to these data, it is thought that mast cells play a more active role in the immune system of partridges in the prepubertal period.