Abstract-OMR systems for test scoring were widely developed as commercial solutions and research topics. The filling area of the answer sheets, found so far, is in form of bubble or lozenge. However, most schools in Thailand use grid answer sheets. This paper proposes the algorithm of test scoring for grid answer sheets. The method used is based on projection profile and thresholding techniques. The proposed method is also able to detect more than one or no selected choice. Among 300 test samples with 3 types of grid answer sheets and total 16500 questions, the average accuracy result was 99.909%, which was considered satisfactory. The error was caused by some pale marks from input rather than the algorithm itself.