The aim of the study was to compare the adaptation of two corresponding single cones to the root canals walls prepared by Revo-S or ProTaper nickel titanium rotary system instruments using fluorescent dye penetration and fluorescent microscope. Materials & Methods: In this study 48 permanent maxillary first and second molars were selected for the study. Samples were divided into 4 experimental groups (n=10): PT8 prepared by ProTaper, RS8 prepared by Revo-S. Both PT8 and RS8 evaluated after 8hours. PT30 prepared by ProTaper, RS30 prepared by Revo-S. Both evaluated after 30 days. Two positive and negative control group (n=4). AH Plus sealer was used in all groups except positive control group obturated without sealer. Obturation was done for each sample with corresponding single cone. All samples were immersed in 2% Rhodamine B solution (fluorescent dye) for 48 hours. Horizontal sections of 2-mm thickness were obtained at the 3 levels (apical, middle and coronal). Examination by fluorescent microscope under x-10 magnification and image analysis software was used to analyze and calculate the gaps filled with fluorescent dye. Three specimens from each third (9 sections) were randomly selected before thinning and examined by scanning electron microscope. Results: Results showed that no statically significant difference between two systems at all levels and two examination periods for 3 levels although ProTaper system show slight better results. The fluorescent microscope as method of evaluation and confirming the results with SEM, results appear to be nearly similar between two methods. Conclusion: The comparison between two systems files; Protaper and Revo-S show near results and both show good adaptation when used with matching single cone as obturating material with resin sealer. Fluorescent microscope is reliable method for detecting gaps around dental filling but do not give detailed or well magnified image as SEM does. Keywords: Adaptation- Single cone technique- Pro Taper system- RevoS system- fluorescent microscope- Rhodamine –B fluorescent dye.