Objective To investigate mechanism involved in the differentiation of FBL-3 cells(eryth-roleukemia cells)induced by dendritic cells(DC). Methods To cultural the FBL-3 cells together with the DC supematant of different concentration for 72 hours,then we used the Wright's staining methed to record the ma-ture monocyte cell population, the transmission electron microscope to observe the ultramicrostructure, the flow eytoraetry to detect the expression rate of the surface molecular CD14. Results The Wright's staining methed, the transmission electron microscope and the flow cytometry all presented that after being induced by the super-natant of the DC ,the FBL-3 cells can partly differentiate into monocytes,inversion monocyte consistent with the personal characteristics. And the intensity of the DC supernatant was connected with interleukin-12. Conclusion The DC supernatant can induce the FBL-3 cells into monocytoid cell, the differentiated cells correspond to monocyte in macro-appearance,uhramicrostructure and phenotype. The competence of the DC supematant are partly concerned with interleukin-12.