Most patients suffer from moderate to severe pain after elective laparotomy. They often require opioids to alleviate their pain. Opiates invariably induce certain side effects and, occasionally, dependence. Intraoperative infusion of lidocaine and low-dose ketamine reduces postoperative pain and analgesic requirements. This study aims to evaluate the effects of simultaneous infusion of lidocaine and ketamine during open abdominal surgery on the postoperative pain severity and analgesic consumption. In this randomized, double-blinded, single-center study that was performed in Iran, 80 patients scheduled for elective open abdominal surgery under general anesthesia were enrolled in two LK and P groups. Group LK (n=40) received lidocaine-ketamine infusion, and group P (n=40) received placebo (normal saline). Both infusions were started thirty minutes after initiation of surgery and were terminated once the surgery was completed. For postoperative pain management, patient-controlled analgesia (PCA), including fentanyl and paracetamol, was administered for both groups. All patients were evaluated for pain visual analogue scale (VAS) and total adjunctive analgesic (diclofenac suppository) consumption within the first 24 hours after the surgery. The data were analyzed using SPSS. <0.05 were considered significant. Intraoperative infusion of Lidocaine and Ketamine resulted in desirable postoperative pain control. Patients of LK group demonstrated a significant reduction in the pain score at 1, 6, 12, 18, and 24 hours after termination of surgery (<0.001). It also resulted in a decreased requirement for postoperative analgesics, as cumulative analgesic consumption was decreased meaningfully in the patients of LK group (<0.001). Intravenous infusion of lidocaine and ketamine during elective open abdominal surgery reduces pain intensity and analgesic requirements in the first 24 hours postoperatively, without major additional side effects.