Objective: To investigate the inhibition of Enterococcus faecalis by calcium peroxide (CaO₂). Methods: The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Enterococcus faecalis by CaO₂ and calcium hydroxide (Ca(OH)₂) were determined by direct exposure tests (n = 10). The inhibition zone of E. faecalis mycoderm treated with CaO₂ and Ca(OH)₂ paste (53% w/w) was observed using agar diffusion tests (n = 20). The inhibition of E. faecalis biofilms by CaO₂/phosphate-buffered saline (PBS) and Ca(OH)₂/PBS suspensions were observed using confocal laser scanning microscopy and the percentages of live bacteria in the biofilms calculated. Results: The MIC of Ca(OH)₂ (4.5 to 5.5 mg/ml) was higher than the MIC of CaO₂ (2.0 to 2.5 mg/ml) (P 0.05), and the MBC of Ca(OH)₂ (14.5 to 15.5 mg/ml) was higher than that of CaO₂ (3.0 to 3.5 mg/ml) (P 0.05). No inhibition zone was observed for Ca(OH)₂ in agar diffusion tests, while the diameter of the inhibition zone around CaO₂ was 8.6 ± 0.4 mm. There were significant differences between groups in the percentages of surviving bacteria in E. faecalis biofilms after treatment (P 0.05): group CaO₂ group Ca(OH)₂ group PBS group BHI. Conclusion: The inhibition of E. faecalis by CaO₂ was greater than that by Ca(OH)₂. Keywords: biofilm, calcium hydroxide, calcium peroxide, Enterococcus faecalis