Recently, retear rate after repair for massive cuff tear have been improved through devised suture techniques. However, reported retear rate is relevant to preoperative atrophy and fatty degeneration. The purpose of this study was to investigate whether preoperative atrophy and fatty degeneration of rotator cuff muscles improve by successful repair. Twenty-four patients with massive rotator cuff tear were evaluated on the recovery of atrophy and fatty degeneration of supraspinatus and infraspinatus muscle after surgery. Atrophy was classified by the occupation ratio and fatty degeneration by modified Goutallier's classification. Both were assessed on magnetic resonance imaging (MRI) before and after the operation. When the cuff was well repaired, improvement of the atrophy and fatty degeneration were observed in a half and a one-fourth of the cases, respectively. In retear cases, however, atrophy and fatty degeneration became worse. Improvement of atrophy and fatty degeneration of the rotator cuff muscles may be expected in the cases with successful achievement of rotator cuff repair for large and massive tear.