Objective : To study the clinical efficacy and safety of lacrimal occlusion by silicone punctal plug in moderate to severe dry eye patient at Thammasat University Hospital. Methods : 40 eyes from moderate to severe dry eye patients are included in the study. Dry eye grading is determined by one ophthalmologist. Silicone plug will be inserted in a lower punctum. One, two and four-week follow up are scheduled. We will compare the conjunctival Fluorescein staining before and after a punctal plug insertion. Patient satisfaction will be evaluated before and after a punctal plug insertion. Study designs: Prospective comparative study. Results : Percent of dry eye grading by Oxford Scheme before a punctal plug insertion at one, two and four week in grade A, B, C, D, E and >E was 0, 0, 0, 60, 40, and 0% respectively. Percent of dry eye grading after a punctal plug insertion at one week was 42.5, 50, 2.5, 5, 0, and 0% respectively Percent of dry eye grading after a punctal plug insertion at two week was 65.8, 34.2, 0, 0, 0, and 0% respectively Percent of dry eye grading after a punctal plug insertion at four week was 73.7, 26.3, 0, 0, 0, and 0% respectively. The results revealed significant improvement of grading of dry eye after inserted silicone punctal plug in 1st, 2nd and 4th week. Comparing dry eye grading between pre-punctal insertion and 1st, 2nd and 4th week post-punctal insertion has been decreased significantly Percent of patient satisfaction grade 1, 2 and 3 in four week follow up was 0, 25 and 75% respectively. Conclusions : The silicone punctal plug is safety and effective in treatment of moderate and severe dry eye. In some patients, qualities of life have been improved by treatment of the silicone punctal plug alone without using any tear supplements or other medications.