A method of inspection for detecting pattern defects in a mask used for transferring a predetermined pattern of regions passing and blocking an exposure beam, comprising the steps of presetting different acceptable defect sizes for a plurality of conditions different in the line and/or space of the pattern, detecting a defect and recognizing the line and space of the pattern at the defect part, selecting an acceptable defect size corresponding to the line and space of the pattern recognized at the defect part and comparing it with the size of the detected defect, and determining a defect larger than the acceptable defect size as a defect requiring repair; a mask defect inspection system for inspection according to the method, and a mask production method including a step of the inspection.