Objectives This study aims to compare the ex vivo fracture resistance of root canal treated (RCT) teeth restored with four different types of fibers under composite resin. Subjects and Methods One hundred and forty extracted mandibular first molar teeth were assigned to seven groups (n=20/group). Group 1 was the control group. In groups 2 − 7, endodontic access and standard Mesio-occluso-distal (MOD) cavities were prepared. Following RCT, group 2 was left unrestored. In group 3, flowable composite resin (FCR) was used to line the cavities and restored with composite resin. In groups 4,5,6 and 7, Ribbond, Everstick, Dentapreg and Bioctris fibers were inserted in flowable resin and restored respectively. Results All the groups restored with fiber reinforced composite displayed higher fracture resistance than the group restored with only composite resin (p<0.001). In addition, Groups restored with Everstick and Bioctris (Groups 5 and 7) showed higher fracture resistance when compared to Ribbond and Dentapreg (Groups 4 and 6). Conclusion E glass fibers demonstrated highest fracture resistance and hence can be preferred over other fiber types to reinforce RCT teeth with weakened crown structures.