Abstract : The aim of study was to evaluate the anti-bacterial effect of four protocols of irrigation solutions (group 1: distilled water, group 2: hypochlorite sodium NaOCl 5.25% + EDTA, group 3: MTAD, and group 4: NaOCl 1.3% + MTAD). The clinical study consists of 52 anterior teeth from 29 adolescent patients (10-16 years). The studied bacteria were: ichirichia colli, SPP and anaerobic bacteria. Group 3 and 4 showed the reduction of an account of ichirichia colli, SPP and anaerobic bacteria after immediate irrigation solutions with superiority of group 3. Group 3 showed the reduction of an account of SPP after 48 hours of irrigation solution. Group 2 showed reduction of SPP + anaerobic bacteria after immediate irrigation solution and reduction of SPP bacteria after 48 hours of irrigation solutions. The new endodontic irrigation solution MTAD examined in this study had good anti-bacterial effect on many bacteria.