Aim: This finite elemental stress analysis (FEA) study was aimed to test the effect of fiber and metal posts on stress distribution in premolar teeth with endodontic–periodontal (EP) lesion. Methodology: Three FEA models representing different EP lesions (primary endodontic disease (PED), PED with periodontal involvement and true-combined) were created. Tooth-model without EP lesion was used as control. The root-canals were assumed as root-filled, restored using glass-fiber or metal posts, resin composite build-up, and ceramic crown. A 300 N load was applied from the palatal surface of the crown with a 135° angle. The SolidWorks/Cosmosworks structural analysis program was used for FEA analysis. Results were presented by considering von Mises criteria. Results: Maximum stress values for PED, PED with periodontal-involvement and true-combined lesions were 2.26, 1.25, 0.74 MPa for glass-fiber post; 2.08, 1.51, 1.18 MPa for metal post, respectively. If there is PED, fiber-post gave an advantage to the tooth at core structure and coronal third of the root. Metal post kept the stress inside its body however caused small, high stress concentrated areas at cervical. When there is PED with periodontal-involvement, metal post forwarded less stress toward the apical while fiber-post saved the coronal structure. In true-combined lesion model, metal post kept the stresses within its body and forwarded less stress toward the remaining root structure and periodontium. Conclusion: EP lesions have an effect on stress distribution therefore the post material selection should be done based on the severity of the lesion. Metal posts might be preferrable since it forwards less stress toward the surrounding periodontal tissues during wound healing.