Introduction: Stem cells have great therapeutic potential due to their capacity for self-renewal and their potential for differentiating into multiple cell lineages. It has been recently shown that the host immune system has fundamental effects on the fate of transplanted mesenchymal stem cells during bone repair, where the topical administration of aspirin is capable of improving calvarial bone repair in rodents by inhibiting tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) production. This study investigates whether aspirin is capable of accelerating the regenerative potential of bone marrow mesenchymal stem cells (BMSC) in a mini swine calvarial bone defect model. Methods: Calvarial bone defects (3 cm x 1.8 cm oval defect) in mini swine were treated with BMSC pretreated with 75 mu g/ml aspirin for 24 h seeded onto hydroxyaptite/tricalcium phosphatel (HA/TCP), or with BMSC with HA/TCP, or with HA/TCP only, or remained untreated. Animals were scanned with micro-computed tomography (microCT) at 2 days and 6 months postsurgery and were sacrificed at 6 months postsurgery with decalcified tissues being processed for histomorphometric examination. The cytokine levels, including TNF-alpha and IFN-gamma, were measured by enzyme-linked immunosorbent assay (ELISA). Results: Aspirin at 75 mu g/ml promoted the osteogenesis of BMSC in vitro and in vivo, shown by Alizarin Red staining and new bone volume in the nude mice transplantation model (p < 0.01), respectively. Defects treated with aspirin-BMSC showed significantly greater new bone fill compared with other three groups at 6 months postsurgery (p < 0.01). Aspirin-BMSC treatment has significantly decreased the concentration of TNF-alpha and IFN-gamma (p < 0.05). Conclusions: The present study shows that BMSC pretreated with aspirin have a greater capacity to repair calvarial bone defects in a mini swine model. The results suggest that the administration of aspirin is capable of improving BMSC-mediated calvarial bone regeneration in a big animal model.