The primary tooth pulpectomy is a common clinical procedure. The choice of filling material is important to the success rate, but antibacterial properties of such materials against organisms known to inhabit infected primary root canals have not been well documented. This study compared the antibacterial effectiveness of 10 materials: 1. Calcium hydroxide mixed with camphorated parachlorophenol (Ca(OH)2+CPC) 2. Calcium hydroxide mixed with sterile water (Ca(OH)2+H2O) 3. Zinc oxide mixed with CPC (ZnO+CPC) 4. Zinc oxide mixed with eugenol (ZOE) 5. ZOE mixed with formocresol (ZOE+FC) 6. Zinc oxide mixed with sterile water (ZnO+H2O) 7. ZOE mixed with chlorhexidine dihydrochloride (ZOE+CHX) 8. Kri paste 9. Vitapex paste 10. Vaseline (control) These materials were compared against microbial specimens obtained from 13 infected primary teeth by using an agar diffusion assay. The results suggest that the materials could be divided into three categories. Category I, with the strongest antibacterial effect included ZnO+CPC, Ca(OH)2+CPC, and ZOE+FC. Category II, with a medium antibacterial effect included ZOE+CHX, Kri, ZOE, and ZnO+H2O. Category III, with no or minimal antibacterial effect included Vitapex, Ca(OH)2+H2O, and Vaseline. There were no significant differences within each category, but there were significant differences between the categories. The one exception was the antibacterial effect of ZOE+FC which was not significantly different from ZOE+CHX, Kri, or ZOE.