An optical proximity correction (OPC) method includes preparing basic data for OPC, measuring with a scanning electron microscope (SEM) an after development inspection (ADI) critical dimension (CD) of a photoresist (PR) pattern with respect to a sample, measuring with the SEM an after cleaning inspection (ACI) CD of a wafer pattern formed using the PR pattern, generating CD data of the sample reflecting PR shrinking caused by the SEM measurement by using the measured ADI CD of the PR pattern and the measured ACI CD of the wafer pattern; and generating an OPC model based on the basic data and the CD data of the sample.