This study evaluated the effect of the addition of the activated charcoal to different formulations of calcium hydroxide on their effect on dentin microhardness of endodontically treated teeth. Ninety one freshly human extracted single rooted teeth were selected. The samples were cleaned and shaped and classified according to the type of the dressing into five groups; Group 1; (21 samples) dressed with calcium hydroxide paste with Iodoform ( Metapex) ( META,Chungcheongbuk-do,Korea ), Group 2; (21 samples) dressed with conventional calcium hydroxide with saline(GAMA dental lab,Cairo, Egypt ). Group 3; (21 samples) dressed with calcium hydroxide paste with Iodoform mixed with activated charcoal ( Eucarbon Sedico, Cairo, Egypt) and Group 4; (21 samples) dressed with conventional calcium hydroxide and activated charcoal with saline and Group 5; Control group (undressed). The samples were further classified according to the observation time into: Subgroup A; (7 samples) after two weeks. Subgroup B;(7 samples) after one month and Subgroup C; (7 samples) after two month. The microhardness measurements were performed using a Vickers Microhardness Tester (Model HVS-50, Laizhou Huayin Testing Instrument Co., Ltd. China). The results showed that there was continuous decrease in the values of dentin microhardness by time however the samples with activated charcoal showed higher mirohardness over the tested periods. It was concluded that the addition of activated charcoal to the calcium hydroxide compounds can decrease the softening effect of different formulations of calcium hydroxide on the root canal dentin.