Purpose: The purpose of this study was to evaluate the healing of an injectable mixture of nanoparticles of magnesium-enriched hydroxyapatite (mHA) in peri-implant defects. Materials and Methods: Thirty-two dental implants were placed in 16 tibiae of eight female Large White pigs. In each animal, four implant beds (two sites each tibia) with medial three-wall intrabony defects were prepared. Via random selection, one bone defect in each tibia was filled with injectable mHA putty (n = 16, test group), whereas the other defect was not filled (n = 16, control group). Two animals were sacrificed after 2 weeks, two after 4 weeks, two after 6 weeks, and two after 8 weeks. In all, 32 block section samples were obtained for histologic and histomorphometric analyses. Results: The test group exhibited statistically significantly higher values for bone-to-implant contact (BIC) and lower amounts of connective tissue (CT) over time. The test group showed a remarkable increase in vital bone values between 6 and 8 weeks after implant placement. After 8 weeks, the injectable mHA was almost completely resorbed. Conclusions: Injectable mHA putty could be a useful and suitable bone grafting material in peri-implant defects. Keywords: animal study, bone graft, hydroxyapatite, magnesium-enriched hydroxyapatite, peri-implant defect