Objective To isolate and identify piroplasms from rodents in Japan by using NOD/shi scid mice, and to test its nature to infect human RBC. Methods The rodents' blood specimens were inoculated into NOD/shi scid mice, whose circulating erythrocytes(RBC) had been replaced with human RBCs(hu RBC SCID mice). Results Babesia microti isolated from rodents proliferated within the human RBCs in the hu RBC SCID mice, and one type was identical to the parasites from human. Conclusion The isolates from rodents were demonstrated to be infective for human erythrocytes by inoculation into hu RBC SCID mice.