A 10-year-old castrated male cross-breed dog was referred for the repair of perineal hernia with bladder retroflexion and a mass lesion in the hernial sac. Surgical treatment was performed and the mass was identified as degenerated adipose tissue that was suspected to be derived from the omentum. The hernial contents were reduced without difficulty, and the dog exhibited a normal recovery. Two days after surgery, the dog suddenly exhibited anorexia and azotemia. Exploratory laparotomy was performed, which showed the dilation of both ureters with discoloration of the bladder serosa and strangulation of the urinary bladder neck. Careful inspection confirmed that a fibrous band, which was connected to the mass-like degenerated adipose tissue, had caused the strangulation. Two days after removal of these tissues, the dog recovered, with normal findings on blood biochemical analysis. The condition described in this report is an uncommon complication of perineal hernia repair. The findings suggest that degenerative fat tissue should be resected during perineal hernia repair in dogs, in order to prevent possible bladder strangulation after surgery.