The patient was a 69-year-old man with localized cT1cN0M0 prostate cancer, who underwent robotassisted laparoscopic prostatectomy (RALP). The operation time was 188 minutes, blood loss was 300 ml, including urine, and no intraoperative complications were noted. The fourth day after RALP, he suddenly complained of nausea and vomiting, and there was right lateral abdominal tenderness. Emergency abdominal computed tomographic scan revealed small intestinal hernia in the right lower abdomen, and we performed emergency laparoscopic surjery. At re-operation, we found lacerations of the peritoneum and transversus abdominis fascia at the insertion site of the 12 mm assistant port, and prolapse of the small intestine. Our diagnosis was lateral port site hernia following RALP. There was no necrosis in the small intestine. The transversus abdominis fascia was Z-sutured through the abdominal cavity with an absorbable thread, and the oblique abdominis muscle was Z-sutured extracorporeally to complete the operation. The patient was discharged on the eleventh day with good progress after re-operation. The possibility of lateral port-site hernia after RALP should be kept in mind, and more reliable port-site closure should be considered.