Background: Enterococcus Faecalis (E faecalis) is isolated usually from failed root canal treated teeth. It can bind to dentin and co-aggregate with other organisms. The organism is resistant to the intracanal medicaments and irrigants. It has the ability to produce biofilms and survive within the root canal. They may develop resistance at different phases of bacterial growth cycle. Objective: To study the effect of chlorine dioxide on different phases of E faecalis growth cycle for 1 and 3 min duration. Methodology: E faecalis ATCC strain (29212) was cultured in different growth phases on dentinal blocks of extracted human teeth. After treatment with chlorine dioxide, left out colonies were counted from dentinal shavings. Observation of the remaining biofilm of different phases was made using the scanning electron microscope and comparison between them was done. Results: In all 3 phases, at the end of 1 and 3 min, significantly (p<0.01, p<0.001 respectively) less E faecalis colonies were observed when compared to initial count. When effect of chlorine dioxide on E faecalis colonies was compared between the three phases, at the end of 1 min, significantly (p<0.05) less E faecalis colonies were observed in exponential phase than in starvation phase. However, the E faecalis colony count during stationary phase was significantly (p<0.05) less than the colony counts in both exponential and starvation phases. At the end of 3 min, there was no significant difference in E faecalis colony count between exponential and starvation phases. However, the E faecalis colony count during stationary phase was significantly (p<0.05) less when compared to the colony counts in both exponential and starvation phases. Conclusion: Our study showed that starved cells of E faecalis were more resistant to 13.8% chlorine dioxide irrigant when treated for 1 and 3min. Keywords: E faecalis, Chlorine dioxide, Dentinal blocks, Biofilms.