In this study, histological and histochemical properties and distrubition of mast cells (MCs) were investigated in the fetal sheep skin. Fetuses were divided into 7 age groups. Skin samples were taken from 35 fetuses of between 56 day and 145 day-old. The samples were fixed in neutral buffered formaline and paraffin sections were cut a thickness of 5 mu m. Tissues were stained with haematoxylin and eosin, toluidine blue (TB) and alcian blue/safranin O (AB/SO). Mast cell numbers determined in a test area (1 mm(2)). Mast cells were firstly recognized in skin of 83 days-old fetuses. The MCs were observed around the blood vessels and hair follicles in dermis. MCs granules were stained with AB in 3(rd) and 4(th) groups also were stained with AB/SO in last three groups. MCs numbers were 2.80 +/- 0.87/mm(2) in 3(rd) group (75(th)-85(th) days), 12.40 +/- 2.03/mm(2) in 4(th) group (85(th)-100(th) days) 22.80 +/- 2.01/mm(2) in 5(th) group (100(th)-110(th) days), 26.00 +/- 1.04/mm(2) in 6(th) group (110(th)-120(th) days) and 27.20 +/- 0.24/mm(2) in 7(th) group (120(th)-145(th) days). The significance between 3(rd)-4(th) groups and last three groups were statistically important (P<0.001).