A method for measuring a reaction rate of a reactive mesogen and an alignment layer formed thereby, the method including coating an alignment material on a substrate. The alignment material includes a backbone and a reactive mesogen connected to the backbone. The reactive mesogen includes an unsaturated bond. The alignment material is irradiated with ultraviolet light, or is heated, to form the alignment layer. A marking compound, including a thiol group is coated on the alignment layer and reacts with remaining unreacted reactive mesogen, to form a marked mesogen. An amount of the marked mesogen is detected. A reactive ratio is measured by comparing an amount of the reactive mesogen before irradiating or heating with an amount of the marked mesogen.