Atlantoaxial dislocation (AAD) is a complex upper cervical spine disorder that often requires C1-2 fusion to achieve durable alignment and neurological protection. Conventional open C1–C2 fusion provides reliable outcomes but is associated with extensive posterior muscle dissection, blood loss, and approach-related morbidity. Minimally invasive posterior atlantoaxial lateral mass joint fusion (MIS-PALF) was developed to mitigate these limitations by utilizing an intermuscular corridor that preserves posterior musculature. With advances in endoscopic spinal surgery, further reduction in surgical invasiveness may be achievable while maintaining the biomechanical principles of posterior atlantoaxial fusion. We describe a novel endoscopic posterior instrumentation technique combined with inter-facet fusion for the treatment of AAD and report early clinical and radiographic outcomes. Two patients with AAD underwent endoscopic posterior C1–C2 instrumentation with inter-facet joint fusion. Using a muscle-sparing posterior intermuscular approach through an approximately 2-cm midline skin incision, direct exposure of the C1–C2 facet joints was achieved under continuous endoscopic visualization. This allowed precise intra-articular cartilage removal, joint surface preparation, and bone graft placement under direct visualization. C1 and C2 screw placement were also performed under endoscopic guidance, in contrast to percutaneous posterior techniques that rely primarily on fluoroscopic navigation. Operative parameters and perioperative complications were recorded. Clinical outcomes were assessed using the visual analog scale (VAS), Neck Disability Index (NDI), and neurological examination. Radiographic evaluation included assessment of atlantoaxial alignment, implant position, and evidence of fusion using postoperative imaging and follow-up computed tomography. Endoscopic posterior instrumentation with inter-facet fusion was successfully completed in both patients without intraoperative complications or neurological deterioration. Blood loss was minimal, and fluoroscopy usage was comparable to that of conventional open posterior procedures and substantially less than typically required for percutaneous instrumentation. Postoperative imaging demonstrated satisfactory reduction of atlantoaxial dislocation and stable instrumentation. At early follow-up, both patients showed significant improvement in neurological status, with radiographic evidence of progressing inter-facet fusion. These preliminary findings suggest that endoscopic posterior instrumentation with inter-facet fusion for AAD is technically feasible and may enhance fusion accuracy while further reducing surgical morbidity.