Disclosed is a fabrication method of a polymeric optic waveguide grating, the method including: forming a core layer of a polymeric material on a substrate; irradiating an ultraviolet ray to the core layer to pre-cure a surface of the core layer; pressing the pre-cured core layer at a predetermined pressure by using a master having a grating pattern; irradiating the ultraviolet ray in a state that the master is pressed, to fully cure the core layer; and separating the master from the fully cured core layer to form a grating pattern on the core layer.