A method of detecting an asymmetric portion of an overlay mark includes forming a plurality of virtual overlay marks having a plurality of virtual asymmetric portions. The virtual asymmetric portions may have different sizes with respect to a reference model profile of a reference overlay mark. Virtual information with respect to each virtual overlay mark may be obtained. The virtual information of the virtual overlay marks may be compared with actual information of an actual overlay mark to identify virtual information of the virtual overlay mark corresponding to the actual information of the actual overlay mark. Thus, measuring the overlay of the actual overlay mark may be performed under than the actual asymmetric portion may be excluded from the actual overlay mark, so that the overlay may be accurately measured. As a result, errors may not be generated in a correcting process to a layer using the accurate overlay.