Abstract Aim: to know ability of Enterococcus faecalis invasion into root dentin. Methodology: Forty single rooted human intact teeth were selected, after access opening and canal debridement, all the samples were subjected for gamma sterilization to ensure complete absence of microorganisms, then exposed to Enterococcus faecalis broth, broth is placed with the help of micro pipette into root canal and also at the same time apical 1/3 of tooth were immersed into broth for 8 weeks, biomechanical preparation, obturation and coronal sealing done using GIC followed by examination under confocal laser scanning microscope after splitting the teeth samples into two halfs buccolingually. Results: This study shows invasion of Enterococcus faecalis upto 160 μm deep in to root dentin. Conclusion: penetration and survival of Enterococcus faecalis deep into dentin in extreme conditions may be the possible reason for persisting infection after root canal treatment.