To isolate and purify peripheral blood lymphocyte-like cells from the arctic lamprey,Lampetra japonica,centrifugation on Ficoll-Paque was performed and a uniform population of leucocytes containing lymphocyte-like cells with the mixture of Ficoll-Urografin solution at proportion of 1.092 was yielded.With the FSC and SSC character of the cells on flow cytometer,lymphocyte-like cells were separated successfully,and the purity was 95.68%.About 2.4×10⁶ lymphocyte-like cells could be purified from 1 ml peripheral blood.Under TEM,lymphocyte-like cells were round or ellipse in shape without microvilla.There were mitochondria with cristae,rough endoplasmic reticulum,dissociated ribosomes and vacuoles in the cytoplasm.Lymphocyte differentiation analysis revealed that there was no evident differentiation of T and B lymphocytes in the leucocytes of L.japonica.