Objective To evaluate the antibacterial efficacy of KaVo KEY laser on Enterococcus faecalis（E. faecalis） within infected root canals and roots surface in vitro. Methods Fifty single-rooted teeth were selected, and infected root canals and roots surface vitro models were prepared. Then, these specimens were divided into three groups. First group were untreated as blank control. The other two groups were the laser groups: Irradiated 15 s and 30 s respectively with 80 mJ and 140 mJ in root canals and on roots surface. Microbiological samples were collected from root canals and roots surface at two time points（before irrigation and immediately after irrigation）. The dentin chips from three different zone of part of root canals in each group were immediately collected and were cultured for 24 h in brain heart infusion（BHI）. Results The number of E. faecalis in root canal and root surface in each of the groups were effectively reduced（P0.05）. Compared with the blank control, the bacterial number in 100 μm of dental tubules decreased after specimens treated with 80 mJ, and the experimental group irradiated 15 s was a significant decease（P
