Objective: Non-steroidal anti-inflammatory drugs (NSAIDs) have shown antibacterial activity in some recent studies. The aim of this study was to evaluate the antibacterial effect of diclofenac against Enterococcus faecalis (E. faecalis) as a resistant endodontic bacterium in comparison with ibuprofen, calcium hydroxide and amoxicillin.Materials and Methods: The antibacterial activity of materials was evaluated using agar diffusion test and tube dilution method. Mixtures of 400 mg/ml of materials were prepared. The bacteria were seeded on 10 Muller-Hinton agar culture plates. Thirty microliter of each test material was placed in each well punched in agar plates. After incubation, the zone of bacterial inhibition was measured. Minimum inhibitory concentration (MIC) of the test materials was determined by agar dilution method. One-way Analysis of Variance (ANOVA) followed by Sidak post hoc test was used to compare the mean zone of microbial growth in the groups.Results: There were significant differences between the two groups (p< 0.05). Results of the agar diffusion test showed that antibiotics (amoxicillin, gentamycin) had the greatest antibacterial activity followed by NSAIDs (ibuprofen, diclofenac). Ca(OH)2 failed to show antibacterial activity. Diclofenac and ibuprofen showed distinct antibacterial activity against E. faecalis in 50 µg/ml and above concentrations.Conclusion: Within the limitations of this in vitro study, it is concluded that diclofenac and ibuprofen have significantly more pronounced antibacterial activity against E. faecalis in comparison with Ca(OH)2.