Oxycodone is a μ‐opioid receptor agonist and is generally indicated for the relief of moderate to severe pain. The aim of this study was to compare the analgesic efficacy of patient‐controlled oxycodone and fentanyl for postoperative pain in patients undergoing colorectal surgery. Patients scheduled to undergo elective colorectal surgery (n=82) were allocated to receive oxycodone (n=41, concentration of 1 mg/mL) or fentanyl (n=41, concentration of 15 μg/mL) for postoperative pain management. After the operation, pain using a numerical rating scale (NRS), delivery to demand ratio, infused dose of patient‐controlled analgesia (PCA), side effects, and sedation levels were evaluated. Median (25%–75%) cumulative PCA dose of oxycodone group at 48 hours (66.9, 58.4–83.7 mL) was significantly less than that of fentanyl group (80.0, 63.4–103.3 mL, P=.037). Six hours after surgery, the mean (SD) NRS scores of the oxycodone and fentanyl groups were 6.2 (2.4) and 6.8 (1.9), respectively (P=.216). The mean equianalgesic potency ratio of oxycodone to fentanyl was 55:1. The groups did not differ in postoperative nausea, vomiting, and level of sedation. Patient‐controlled oxycodone provides similar effects for pain relief compared to patient‐controlled fentanyl in spite of less cumulative PCA dose. Based on these results, oxycodone can be a useful alternative to fentanyl for PCA in patients after colorectal surgery.