Abstract: 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 at a high percentage is sustained for a long period of time. 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, When a medium to large mammal 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.