Aim To compare the antimicrobial effect of 2% chlorhexidine, 2.5% sodium hypochlorite and MUMS containing 2% chlorhexidine. Materials and methods All of the above irrigants were examined on Enterococcus faecalis, Streptococcus mutans, Candida albicans, Lactobacillus casei and E.coli. A total of 0.5 CC of each solution and 0.5 CC of McFarland solution bacterium were added to each examination tube. After 15, 30 and 45 minutes, colony count was performed for each tube. The difference in the number of bacteria indicated the effect taken by disinfectant material. Results MUMS containing chlorhexidine showed the antimicrobial properties just like chlorhexidine's effect against E.coli, Streptococcus mutans, Candida albicans, Enterococcus faecalis and Lactobacillus casei in preventing these entire microorganisms to incubate. Sodium hypochlorite was not effective against Enterococcus faecalis and Candida albicans incubated in 15, 30 and 45 minutes and Enterococcus faecalis in 15 minutes. Conclusion MUMS has antimicrobial properties similar to chlorhexidine. Clinical significance As MUMS containing chlorhexidine can transfer chlorhexidine through its own surfactant around apical area and it can open the dentinal tubules by its own chelator for more penetration of chlorhexidine, it may be a choice for canal irrigation. How to cite this article Bidar M, Hooshiar S, Naderinasab M, Moazzami M, Orafaee H, Naghavi N, Jafarzadeh H. Comparative Study of the Antimicrobial Effect of Three Irrigant Solutions (Chlorhexidine, Sodium Hypochlorite and Chlorhexidinated MUMS). J Contemp Dent Pract 2012;13(4): 436-439.