Purpose: To study the stability and the peri-implant alveolar bone response of immediately loaded micro-implants. Materials and Methods: Micro-implants were implanted into the mandibles of male beagle dogs, immediately loaded in the test group (200-g horizontal force) and unloaded in the control group. The healing bone was then labeled with polyfluorochrome at intervals over 10 weeks. Radio-graphs were taken at the beginning and end of the study. Seventy-three days after implantation, the dogs were euthanized, and the dissected mandibles were prepared for examination. The tissue specimens were evaluated by light microscopy, fluorescent microscopy, polarized light microscopy, scanning electron microscopy, and energy dispersive x-ray spectroscope. Results: The teeth anchored by the micro-implants moved normally, while the micro-implants remained basically stable. All the microscopy results showed that osseointegrated interfaces were formed between the micro-implants and the alveolar bone. Fluorochrome labels demonstrated that lamellar bone had appeared at 6 weeks after implantation, and was formed more extensively after another 3 weeks. Conclusion: This in vivo study found that the stability and osseointegration of immediately loaded micro-implants were not impaired. Micro-implants inserted in dense cortical alveolar bone in the mandibles of beagle dogs may be loaded immediately in a dog model to achieve satisfactory orthodontic anchorage. Keywords: bone-implant interface, immediate loading, micro-implant, osseointegration, stability