The present study evaluated the antibacterial effects of aqueous and gaseous ozone in human root canals infected with Enterococcus faecalis. Infected root canals were divided into two control groups (saline, sodium hypochlorite) and three experimental groups (manual or ultrasonic technique of aqueous and, gaseous ozone). Disinfection procedures were performed, remaining microbial colonies were counted and data were evaluated. Sodium hypochlorite showed the highest antibacterial effect on root canals infected with Enteroccous faecalis. Moreover, aqueous ozone with ultrasonic technique appear to be more influential than aqueous ozone with manual technique and gaseous ozone.