Background: Endodontically treated teeth are subjected to discoloration which must be treated for aesthetic purposes without weakening of tooth structure. Methods: Intra-coronal bleaching using different bleaching agents was tested for affecting the fracture resistance of teeth in three different groups, group 1(n=17) treated with sodium perborate, group 2 (n=17) treated with spirulina extract using photodynamic theory and group 3 (n=17) control group without bleaching. Fracture resistance of single rooted extracted premolar teeth were tested using universal testing machine under a compressive load of 135 degrees on the palatal aspect of the tooth until fracture. Results: Statistical analysis revealed no significant difference between bleaching protocols on fracture resistance of endodontically treated teeth, but they were significantly lower than the nonbleached control group. Conclusions: Bleaching of endodontically treated may compromise the fracture toughness and structural integrity of dentine after root canal treatment with both the conventional bleaching protocol and the photodynamic theory bleaching.