The aim of this study was to determine histologie, histochemical and functional properties of the mast cells of dog intestinal mucosa. For this purpose, 11 mongrel dogs were used. The dogs were divided into two groups; the first group was determined as naturally infected with intestinal parasites (n = 7) and the second group in which no intestinal parasitic infection could be de-termined (n=4). The tissue specimens of the jejunum were obtained by abdominal surgery from both groups; the first specimen collection carried out fallowing a feces examination, than all animals were treated with antiparasitic agents, and 60 days later the second specimen collection was made. Each specimen was divided into two pieces which were placed in both neutral buffered formalin (NBF) and isotonic formalin asetic acid (IFAA) fixatives. To demostrate the mast cells, tissue sections were stained with toluidin blue (TB) and alcian blue /safranın O (AB/SO) methods. The mast cells could not be demonstrated in NBF fixed tissues sufficiently. In contrast to this, the cells were extremely well preserved in (FAA fixed tissues. The mast cells were observed as TB(+), AB(+) / SO(-). There were more mast cells in L. propria compared with submucosa and T. musculuris. The number of mast cells were found to be higher in naturally infected dogs and were dec-reased after antiparasitic treatment, especially in villus intestinales. It was sug-gested that the mast cells in the dogs intestinal mucosa, which are sensitive to formalin, stained AB (+) and SO (-) and increased in respons to parasites, could be concluded as mucosal mast cells.