Objective To study the expression pattern of RYK in the pathway of developmental corticospinal tract projection and provide hints for further study on RYK's function involved in this processes.Methods By In situ and immuno-fluorescence histochemistry,we examined the RYK expression pattern in the developmental murine motor cortex and the projection of corticospinal tract at various time points of E14.5、 E16、E18.5 and postnatal P3、 P5、P7.Results The motor cortex the RYK expression started at E18.5 stage and enhanced gradually at P0 stage.Moreover from P0 to P5 stage the RYK expression also appeared in the pathway of developmental corticospinal tract and decreased gradually after that.Conclusion RYK's expression is closely related to the corticospinal tract projection during its development stage.