Introduction: Pain management is one of the most essential components of postoperative care. Nowadays, the common treatment methods for pain include the use of two large groups of analgesics, namely opioids and nonsteroidal antiinflammatory drugs (NSAIDs). Therefore, the present study aimed to compare the effects of ketorolac (i.e., a noninflammatory drug) and pethidine (i.e., a synthetic opioid pain medication) on pain and complications due to hemorrhoidectomy. Methods: This randomized controlled trial included 90 patients with hemorrhoids who underwent hemorrhoidectomy at Imam Reza Hospital in Birjand, Iran, from May 2017 to 2018. The participants were assigned into two groups, namely ketorolac group who received ketorolac therapy and pethidine group who received pethidine. The severity of pain and complications were measured immediately, as well as at 6, and 12 hours after surgery in both study groups. The quantitative data were expressed as mean and percentage. Data analysis was performed using SPSS software (version 22.0) through Mann-Whitney, Friedman, and Chi-square tests. A p-value less than 0.05 was considered statistically significant. Results: According to the obtained results, out of 90 patients with hemorrhoid, 70.3% were males. The mean age of the participants was 48.29±8.8 years, and there was no significant difference between two study groups regarding age (47.2±8.7 years in the pethidine group, and 49.4±9 years in the ketorolac group, P=0.196). In the ketorolac group, the mean pain scores were 2.33±1.36, 2.28±1.00, and 1.57±0.75, immediately, as well as at 6, and 12 hours after surgery, respectively. In addition, in the pethidine group, the mean pain scores were obtained at 3.15±1.61, 2.64±1.00, and 1.97±0.69, immediately as well as at 6, and 12 hours after surgery, respectively. Accordingly, the pain level was significantly lower in ketorolac group, compared to that in the pethidine group (P<0.05). However, the pain level was higher at 24 hours after surgery in ketorolac group than that in the pethidine group; nevertheless, the difference was not statistically significant (P=0.996). Conclusions: The findings of the present study suggest more significant therapeutic effects of nonsteroidal NSAIDs, compared to opioid drugs on pain after hemorrhoidectomy.