Purpose: To compare the clinical and radiological result of arthroscopic Mattress Locking suture repair to that of a Simple suture repair with small and medium-sized rotator cuff tears. Materials and Methods: Among 92 patients who were followed up after arthroscopic repair in patients with small and medium-sized rotator cuff tear from April 2007 to October 2010, 27 patients who took Arthroscopic Mattress Locking suture were set as group I and 65 patients who took Simple suture were set as Group II. The average age of patients were 58 years old and average follow-up period was 30 months. For analysis, VAS, ASES and KSS were used to analyze the range of joint movement and pain. And, for the image result, MRI performed after operation were evaluated. Results: The average VAS, KSS, UCLA score and ASES prior to surgery improved in the last follow-up (p<0.001), while was no difference in two groups (p>0.001). In MRI follow-up examination, the 2 cases (7.41%) of group 1 showed increased rupture lesions with improved symptoms. And the 12 cases (18.47%) of group 2 showed increased rupture lesions with improved symptoms. Retears in the group I were significant less than the group II (p<0.001). Conclusion: Comparing patients with small and medium-sized rotator cuff tear who took arthroscopic mattress locking suture repair to those who took simple suture repair after over one year follow up period, the clinical result showed no significant difference between two groups. However, Mattress Locking suture repair showed excellent radiological result compared to simple suture repair when comparing rerupture.