Background: Many researchers have tried to enhance materials functions in different aspects of science using nano-modification method, and in many cases the results have been encouraging. To evaluate the histopathological responses of the micro-/nano-size cement-type biomaterials derived from calcium silicate-based composition with addition of nano tricalcium aluminate (3CaO.Al 2 O 3 ) on bone healing response. Material and Methods: Ninety mature male rabbits were anesthetized and a bone defect was created in the right mandible. The rabbits were divided into three groups, which were in turn subdivided into five subgroups with six animals each based on the defect filled by: white mineral trioxide aggregate (WMTA), Nano-WMTA, WMTA without 3CaO.Al 2 O 3 , Nano-WMTA with 2% Nano-3CaO.Al 2 O 3 , and empty as control. Twenty, forty and sixty days postoperatively the animals were sacrificed and the right mandibles were removed for histopathological evaluations. Kruskal-Wallis test with post-hoc comparisons based on the LSMeans procedure was used for data analysis. Results: All the experimental materials provoked a moderate to severe inflammatory reaction, which significantly differed from the control group ( p < 0.05). Statistical analysis of bone formation and bone regeneration data showed significant differences between groups at 40- and 60- day intervals in all groups. Absence of 3CaO.Al 2 O 3 leads to more inflammation and foreign body reaction than other groups in all time intervals. Conclusions: Both powder nano-modification and addition of 2% Nano-3CaO.Al 2 O 3 to calcium silicate-based cement enhanced the favorable tissue response and osteogenesis properties of WMTA based materials.