The present invention discloses a novel means capable of producing a blood chimeric animal in which a state of retaining blood cells originating in a heterologous animal, such as a human, at a high percentage is sustained for a long period of time, even in cases where a medium to large domestic animal is used as a recipient. The method for producing a non-human animal that retains blood cells originating in a heterologous animal, according to the present invention, comprises transplanting hematopoietic cells of a heterologous animal into a non-human animal, in which hematopoietic cells the function of a gene that acts on the hematopoietic system is modified. The gene that acts on the hematopoietic system is, for example, Lnk gene. According to the method of the present invention, when a medium to large mammal such as a pig is used as a recipient, the survival rate of hematopoietic cells originating in a heterologous animal is dramatically increased such that blood chimerism of 10% or more can be maintained even in a 16 month old animal.