Objectives To evaluate the effect of metrinidazole treatment after conventional hemorrhoidectomy pain in patients with third and fourth degree hemorrhoids. Methods We searched the Cochrane Library (Issue 1 2009), PubMed (1966 to March 2009), EMbase (1974 to March 2009), SCI (1974 to March 2009), CBM (1978 to March 2009), CNKI (1994 to March 2009), and VIP (1989 to March 2009) to identify randomized controlled trials or quasi- randomize controlled trials of metronidazole versus placebo for treating post hemorrhoidectomy pain. We evaluated the quality of the included studies by using the Handbook 4.2.6 recommend standards and analyzed data using the Cochrane Collaboration’s RevMan 4.2.10. Results We included seven randomized controlled trials or quais-randomized controlled trials (n=553). Meta-analyses showed that there were statistical differences between metronidazole and placebo in pain after hemorrhoidectomy and the use of an additional dose of analgesia. Conclusions The current evidence shows that metronidazole relieves the pain after conventional hemorrhoidectomy and reduces the additional used of analgesics. Further high quality, large sample randomized controlled trials should be carried out.