The Long-Evans Cinnamon (LEC) rat is an animal model of Wilson’s disease. The rat has a mutation in the copper (Cu)-transporting P-type ATPase (Atp7b) gene that is homologous to the human Wilson’s disease gene, ATP7B. The LEC rat shows all of the biochemical features of the disease. In this study, we focused on the expression levels of mutant Atp7b mRNAs in the peripheral blood mononuclear cells (PBMCs) of the LEC rats. Using quantitative real-time polymerase chain reaction (quantitative RT-PCR), we analyzed the expression levels of Atp7b mRNAs in the PBMCs cells of both the LEC rats and Long-Evans Agouti (LEA) rats, the latter being utilized as a control for the LEC rat. At the ages of 5 and 8 weeks, the inductions of Atp7b mRNA were manifested in the PBMCs of both male and female LEC rats, while their levels in the livers were significantly lower than those of the LEA rats. These results suggest the diversity of cell-physiological and endocrinological Cu metabolisms between the PBMCs and the livers of the LEC rats. Our findings indicate the possibility of a novel Cu metabolism in the cardiovascular network that is concerned with Atp7b of the PBMCs.