ObjectiveTo examine the cause of failure of mitral valve repair. MethodWe retrospectively anal-yzed the clinical data of 89 consecutive patients with non-rheumatic mitral valve diseases who underwent reoperation for failure of mitral valve repair in our hospital from January 2009 through January 2016. There were 54 males and 35 females at age of 36.2±17.4 years. ResultsThere were 16 patients with reoperation of mitral valve repairs and 73 patients of mitral valve replacements. The failure reasons of initial mitral valve repair were technique-related in 63 patients (70.8%) and valve-related in 18 patients (20.2%). Technique-related causes of repair failure included leaflet suture dehiscence (20 patients, 22.5%), edge-to-edge procedure (11 patients, 12.4%), leaflet thickening or retraction (11 patients, 12.4%), ring dehiscence (8 patients, 9.0%), inappropriate annuloplasty (6 patients, 6.7%), incomplete repair (4 patients, 4.5%), and chordal elongation or rupture (3 patients, 3.4%). Median interval since previous repair was 4.0 (0.04-18.0) years for the technique-related failure group, and 9.7 (0.21-35.6) years for valve-related failure group (P < 0.05). ConclusionTechnique-related factors are main causes of repair failure, which include leaflet suture dehiscence, edge-to-edge procedure, and leaflet thickening or retraction. Reoperation for technique-related failure needs to be adopted early.