Mast Cells participate in immediate and late hypersensitivity activities, immunoregulation and inflammation. Recently two groups of them have been detected on the basis to its morphology, content of granules and function: a) Those who are localized in connective tissue and b) Those of the intestinal mucosa. Those of the intestinal mucosa are T dependent and proliferate in parasitic as well as in intestinal hypersensitivity conditions to diverse antigens, in turn, Peyer's Patches (PP) are considered antigen catcher and initiators of intestinal immune responses; these are subject to the influence of diverse substances, several of which are within mast cells (for example: histamine, prostaglandins, etc); for which in this work we investigate the morphology relation between PP and mast cells. Balb/c mice small intestine segments with muscular layer and PP of proximal, middle and distal levels where studied; were histologically processed, toluidine blues stained and mast cells counted in different intestinal layers (PP underlying zone, rest of the muscular, corium and submucosa. Data were analyzed by the paired double T test for mean differences. A greater Quantity of mast cells were observed at the marginal zone of the PP in comparison to the rest of the muscular layer, submucosa and corium. The abundance of mast cells in relation to the PP possibly indicates its modulatory influence on the function of lymphoid cells of the PP.