Objective To observe whether endomorphin-2-immunoreactive (EM2-ir) neurons in the trigeminal ganglion(TG) project to the medullary dorsal horn(MDH) in the rat. Methods Fluoro-gold(FG) retrograde tracing and immunofluorescent histochemical staining for EM2 were applied. Results After FG was injected into the MDH, many FG labeled neurons with small,medium and large diameters were observed in the TG.There were also aboundant EM2-ir neurons with different diameters in the TG.The majority of FG labeled neurons in the TG showed EM2-immunoreactivities.Almost all of the EM2/FG double-labeled neurons were medium and small in size.Conclusion EM2-ir neurons in the TG project to the MDH in the rat.