Xenotansplantation has become a global focus because it may solve the formidable problems in allotransplantation, that is, the donor source. Hitherto clinical xenotransplantion has been in the stage of research with limited cases and unsatisfactory results. The difficulties which hinder the progress of xenotransplantation include: the ideal animal donor has not been found, it is rather difficult to control the rejections (hyperacute rejection, acute vascular rejection, perhaps acute cellular rejection and chronic rejection) after xenotransplantation compared with those after allotransplantation, some animal diseases might be transmitted to and do harm to human recipients, even the community. It is still unknown whether the functions of animal organs can substitute those of human organs permanently. Transgenic pigs on research and various measurements to suppress humoral and cellular immunity may be helpful in overcoming the problems of xenogeneic rejections. Animal diseases should be prevented, screened and treated, and animal models should be established to study the possibility of satisfactory working of animal organs in human body before clinical xenotransplantation is widely practised.