Endodontically treated teeth can be restored with prosthetic crowns over cast metal cores or prefabricated posts with composite resin cores. Prosthetic failure is frequently observed possibly due to microleakage. To verify the influence of the core materials in the microleakage of cast crowns, this research studied three experimental conditions: (a) teeth with partial dental remaining core with prefabricated post and partial composite resin cores, (b) teeth with cast metal posts/cores, and (c) teeth with prefabricated posts and composite resin cores. Teeth preparations were standardized, duplicated and the crowns were made in NiCr alloy, which were cemented with zinc phosphate cement. The specimens were submitted to thermocycling and mechanical stresses. They were immerged in a 0,05% aqueous solution of basic fuchsin for 8 hours during 3 days. The crowns were sliced buccal-lingually, and their microleakage was evaluated by glass magnification, according to a score scale. There was no statistical difference between conditions (a) and (c). Microleakage at cervical region of axial wall was observed in both cases. Condition (b) showed higher microleakage, which reached medium third of axial wall.