Purpose The purpose of this study was to compare clinical outcomes of the arthroscopic rotator cuff repair (ARCR) in posterosuperior massive rotator cuff tears with or without arthroscopic suprascapular nerve (SSN) decompression in terms of arthroscopic release of the transverse scapular ligament. Methods Patients with a minimum follow-up of 24 months who underwent complete repair of torn rotator cuff involving a complete full-thickness tear of the supraspinatus and the infraspinatus were retrospectively evaluated. A total of 31 patients were treated with SSN decompression (group 1), and 36 patients were treated without SSN decompression (group 2). The clinical and functional outcomes were evaluated using the University of California, Los Angeles (UCLA) score, active range of motion (flexion and external rotation), and a visual analog scale (VAS) for pain. Repair integrity and fatty infiltration of the repaired cuff were examined by MRI. Results There was no significant difference between both groups across all measured at final follow-up: UCLA scores were 30.8 in group 1 and 30.8 in group 2 (p = 0.58); VAS scores were 14 mm and 13 mm, respectively (p = 0.35); active flexion angle were 149 degrees and 153 degrees, respectively (p = 0.35); and external rotation angles were 41 degrees and 42 degrees, respectively (p = 0.85). There were no significant differences in the re-tear rate (42% in group 1 and 33% in group 2, P = 0.75) and post-operative fatty infiltration scores of supraspinatus (P = 0.28) and infraspinatus (P = 0.37) in both groups. Conclusions The functional outcomes and healing rate did not differ significantly between the groups with or without SSN decompression treated with arthroscopic cuff repair for massive RCT. At the short-term follow-up, SSN decompression was not found to have significantly affected the outcome of ARCR for posterosuperior massive RCT.