The research objective was to study a morphofunctional condition of mast cells of placenta in pigs, in the norm and during pathologically proceeding pregnancy. The results of histological and ultramicro- scopic research of pigs’ placenta tissues at physiologi- cally proceeding and complicated pregnancy were giv- en. The material was selected on the farm of Dergacheva (Sverdlovsk Region, Polevskoy town). The research was conducted at the Department of Morphol- ogy, Examination and Surgery of Ural State Agrarian University. The placentae from 25 pigs, with pathology of stillbirth, mummification and combined pathology were investigated. The estimation of morphological changes was made in stillbirth and mummification for three components of placenta: cytotrophoblast, vascular link and connective tissue. Quantity and quality standard of mast cells in placenta of pig was made. It was estab- lished that at pathologically proceeding pregnancy the shortening of the villi of the chorion, epithelial prolifera- tive activity, areas of necrosis of the villi, the deposition of fibrinoid in majorsince space were marked. Vascular reaction was manifested in the overgrowth of blood ves- sels, mass diapedesis of red blood cells, endothelial cell exfoliation, intravascular hemolysis of red blood cellsand the formation of intravascular blood clots. In pigs with combined pathology in the zones of necrotic disin- tegration of tissues the centers of hemorrhages were localized. From the side of connective tissue component in pigs with stillbirth edema of the villous stroma was observed. It was revealed that the population of mast cells per unit area increased in the presence of patholo- gy of fruiting. In physiological course of pregnancy, sin- gle mastocytes were localized. At physiological course of pregnancy, single mastocytes were localized mainly perivascular. The reaction of mast cells to pathological focus was manifested in the form of active degranula- tion. The highest degree of degranulation activity was observed in the presence of mummified fruits. The se- cretion was of directed character towards necrosis cen- ters.