Objective: The aim of this study was to evaluate bacterial microleakage of the root canals irrigated with different irrigation solutions and the potassium-titanyl-phosphate (KTP) laser system and filled with gutta-percha and AH26 root canal sealer. In addition, the effect of the irrigation solutions on dentin surface was evaluated with a scanning electron microscope (SEM). Background data: A few studies have reported that KTP laser has the capacity to remove the smear layer. Many researchers have demonstrated that propolis has a bactericidal effect. Both are important effects on root canal treatments. Materials and methods: One hundred and twenty single-root single-canal mandibular premolar teeth were used for this study. The root canals were prepared by Dentaport Root ZX and ProTaper rotary instruments with the crown-down technique. The specimens were randomly divided into five groups of 20 teeth each. Each group was irrigated with 17% ethylenediaminetetraacetic acid (EDTA), 20% propolis, 2.5% sodium hypochlorite (NaOCl), 2% chlorhexidine gluconate (CHX), and KTP laser, respectively. A total of 20 teeth were used as controls-10 positive controls and 10 negative controls-which were irrigated with distilled water. The root canals were filled with gutta-percha and AH-26. The external surfaces of specimens were covered with three layers of nail varnish except the apical third. The teeth were inserted into Eppendorf plastic tubes and suspended in glass bottles containing sterile broth. All specimens were inoculated every 5 days with Enterococcus faecalis. The contamination onset time was continuously recorded, as turbidity was the first indication of contamination in a period of 30 days. Results: All statistical analysis was performed using the SPSS for Windows version 15.0 software. A chi(2) test was computed and the statistical significance was set at p < 0.05. The controls behaved as expected. Conclusions: This study showed that different irrigation solutions and KTP laser allowed microleakage of E. faecalis.