Introduction: In endodontically treated teeth with less remaining tooth structure posts are inserted to provide stability and retention for a core. The posts retention is dependent on various factors related to post like- cement post and cement dentine interaction, type of luting cement, and taper of the post. Aim: This in-vitro study aimed to evaluate the effect of endodontic taper on post retention using parallel-sided prefabricated posts luted with dual-cure resin cement. Methodology: Sixty freshly extracted human maxillary central incisors of approximately the same sizes were selected for this study. The Crown of these teeth was separated at the cementoenamel junction and divided randomly into six groups of ten teeth each. Biomechanical preparation was carried out using different tapered Ni-Ti file systems ranged as 0.02, 004, 0.06, 0.08, 0.10, and0.12 taper. Root canal obturation was done with gutta-percha using the lateral condensation method. Results: Taper 0.02 represents the taper size where a smaller average force was required to remove the post from the root canal. The average force required to remove the post from the root in taper group 0.02 was statistically different from all other taper sizes. Taper size 0.04 required highest average force to remove the post. Average force for size 0.04 was statistically different from the taper size 0.02, 0.06, 0.08, 0.10, 0.12 tapers. Conclusion: The result of the present study indicates that increasing taper of root canal adversely affect the post retention. The findings of this study indicate that instrument taper size preparation of the canal makes a difference to resistance to post dislodgement.