Objective determination of tumor region of interest (ROI) on MR images is expected for quantitative analysis of tumors. We developed a semi-automatic method of ROI delineation. We applied this method to head and neck squamous cell carcinoma and evaluated the matching of the ROI delineation by our method and an experienced radiologist. The ADC values were compared for different ROI delineation methods. Averagely, 80% of the area of the ROI matched and the difference of the ADC value was within 2% (sd), showing that our new method of tumor delineation can be used to analyze the tumor characteristics quantitatively.