Abstract: Sbujective: Interspecific embryo transfer could be a valuable tool in preservation programs of endangered species. The majority of previous studies focused on descriptions of microstructure and anatomic differences between intraspecific and interspecific pregnancy, while the report for molecular mechanism of these phenomena was few. The aim of this work was to illuminate the difference of immunological reaction between intraspecific and interfamily pregnancy and to primarily grope for the possible reasons of interfamily pregnant abortion. Methods: The fetuses of interfamily pregnancy day 4, day 8 and day 12 were acted as experimental group, while the ones of intraspcific pregnancy day 4, day 8 and day 12 of embryo transfer and the uteri of pseudopregnant mice of corresponding time were employed as positive and negative groups respectively. Results: The indirect immunofluorescence and laser confocal scan results of cryosections showed: Expressive positions and intensities of MHC class Ⅱ molecules and Gal-α-Gal epitopes were all different in interfamily pregnancy, positive and negative controls in pregnancy day 8.The expressions of MHC class Ⅱ molecules in interfamily pregnancy were weaker than in intraspecfic pregnancy in day 8, and expressive modes in day 12 were also different. Gal-α-Gal epitopes did not expresse in interfamily pregnancy day 8, but in intraspecific pregnancy they expressed in a certain level. In pregnancy day 12, they expressed in a certain degree in interfamily pregnancy, but their expressive modes were different to those in intraspecific pregnancy. Conclusion: These results indicated the differences between interfamily and intraspecific pregnancy. It was possible that these different expressions of MHC class Ⅱ molecules and Gal-α-Gal epitopes would be one of reasons leading to the failure in interfamily pregnancy.