This study evaluated the effect of diode laser treatment for root canal disinfection on fracture resistance and micro-hardness of the tooth. Sixty freshly extracted mandibular and maxillary premolars were accessed under coolant then root canals were flared up to apical preparation size 40 MFA coupled with 5.25% NaOCl as an irrigant. Teeth were divided into two groups, control group (groupI) and lased group (group II) that was lased by diode laser with average power 2w through fibrooptic into the canal 2mm shorter than the apex. Each tooth was embedded in acrylic block then subjected to the fracture resistance test .Each root was then sectioned transversely and polished to record dentin Vickers hardness. Data was analysed with student t-test then with linear regression test. The Lased samples presented a significantly higher resistance to fracture than unlased samples. There was no statistically significant differences found between Vickers hardness (HV) of lased and unlased samples and there was no relation between fracture resistance and hardness. So it was concluded that: 1. Diode laser (980nm) treatment had no adverse effect on dentin microhardness 2. Diode laser (980nm) treatment increased the fracture resistance of dentine. 3. Diode laser (980nm) treatment could attain better functionability and maintenance of tooth after endodontic treatment.