We compared the effects of preoperative administration of diclofenac sodium, celecoxib, and acetaminophen on postoperative pain in patients undergoing minor oral surgery under general anesthesia. One hundred twenty-eight patients were randomly divided into 4 groups preoperatively treated with diclofenac sodium 50 mg, celecoxib 400 mg, acetaminophen 1000 mg, or placebo. Postoperative pain was managed using intravenous patient-controlled infusion of fentanyl. Assessments included levels of postoperative pain by using visual analog scale (VAS) scores at 4, 5, and 6 hours after administration of the test drug; consumption of fentanyl up to each time point; and time to first requirement for fentanyl. Our study demonstrated that, for diclofenac sodium and celecoxib in comparison with placebo, there were significantly lower VAS scores at 4, 5, and 6 hours after oral administration of the study drug; a longer period of time to first requirement for fentanyl after surgery; and less consumption of postoperative fentanyl. A similar analgesic effect versus placebo was noted for acetaminophen but only at the 5- and 6-hour time points. In contrast, no significant differences in VAS scores at 4 hours after administration or time to first requirement for fentanyl were observed between acetaminophen and placebo. Furthermore, no significant differences in measurements were observed between the study drugs at any time point. These findings suggest that oral administration of celecoxib 400 mg is suitable for controlling postoperative pain, and as effective as diclofenac sodium 50 mg. Acetaminophen 1000 mg also exerts analgesic effect with slower onset for postoperative pain.