The purpose of this investigation was to evaluate the effect of osteoprotegerin (OPG)-modified autologous bone marrow stromal cells (BMSCsOPG) combined with guided tissue regeneration on bone regeneration of periodontal window defects. pSecTag/2B-OPG was transduced into BMSCs by Lipofectamine 2000. The expression of OPG protein in the BMSCs was detected by immunocytochemistry and Western blotting. Periodontal window defects (4 × 4 × 3 mm) were surgically created in the buccal aspect of the mandibular premolars and randomly assigned to receive BMSCsOPG-PLGA (cells + material + OPG), BMSCs-PLGA (cells + material), PLGA (material), or root planing only (negative control). The animals were euthanized at 6 weeks postsurgery for histologic analysis, and histologic measurements were then performed. Results showed that the height of new alveolar bone and cementum and the formation of new connective tissue were significantly greater in the experimental group than in the control groups after 6 weeks (P .05), whereas there was no significant difference between the material control and negative control (P > .05). These findings suggest that delivery of BMSCsOPG-PLGA may be a viable approach to promote bone regeneration of periodontal bone defects.