Background: Oral metronidazole has been previously demonstrated to decrease postoperative pain after open hemorrhoidectomy. The aim of this study was to evaluate the effect of topical metronidazole in reducing postoperative pain of hemorrhoidectomy.Methods : In this double-blind, clinical trial forty 20- to 40-year old male patients were scheduled for hemorrhoidectomy under spinal anesthesia at the Imam Khomeini Hospital in Urmia, Iran from April to September 2010. The participants were assigned to receive topical metronidazole (n=20) or placebo (n=20). Pain intensity was assessed using a visual analog scale (VAS), the time of first narcotic request and morphine administrations were also recorded. Results : The VAS scores were lower in metronidazole than the control group but this difference was not statistically significant, except after 24 hr post-surgically. Morphine administration in the first 24 hr was lower in the metronidazole group (P<0.05).Conclusion: Although metronidazole could not prolong the time of first analgesic request, but application of metronidazole gel is associated with lower analgesic requirement.