Abstract : The work aims to compare the influence of irrigation solution MTAD when activated by laser and without activation on the root dentin micro-hardness (MH). Thirty root samples were prepared into two equal halves for dentin MH measurements. The sixty root halves were subdivided equally into three groups (twenty samples each) according to the utilized irrigation solution: MTAD activated by laser, MTAD non-activated by laser and deionized water (control group). Samples from each group were used for dentin MH determination at baseline determination and next to treating to evaluate the variation in MH. Data were analyzed by one-way ANOVA and student's t-test for MH. MTAD non-activated by laser displayed the highest significant lowering in dentin MH (P<0.5). The values of the MH of radicular dentin were higher when MTAD activated by laser used. The results revealed that MTAD activated by laser was the most efficient treatment. Further clinical tests are necessary for establishment of the efficiency, safety and biocompatibility of this treatment prior to be utilized normally in vivo.