Background To introduce a novel transoral instrumentation in the treatment of unstable fractures of the atlas. Methods From January 2008 to May 2018, 22 patients with unstable C1 fractures who received Jefferson-fracture reduction plate (JeRP) via transoral approach were retrospectively analyzed. The case history and the radiographs before and after surgery were noted. The type of fracture, the reduction of the fracture, and position of the internal fixation were assessed through preoperative and postoperative CT scans. Results All 22 patients successfully underwent anterior C1-ring osteosynthesis using the JeRP system, with a follow-up of 26.84 ± 9.23 months. Among them, 9 patients had transverse atlantal ligament (TAL) injury, including 3 in Dickman type I and 6 in type II. The preoperative lateral mass displacement (LMD) decreased from 7.13 ± 1.46 mm to 1.02 ± 0.65 mm after the operation. Bone union was achieved in all patients without implant failure or loss of reduction. There were no surgery-related complications, such as wound infection, neurological deficit, or vertebral artery injury. However, atlantoaxial dislocation occurred in 3 patients with Dickman type I TAL injury 3 months postoperatively without any neurological symptoms or neck pain. Conclusions Transoral C1-ring osteosynthesis with JeRP is an effective surgical strategy to treat unstable atlas fractures with a safe, direct, and satisfactory reduction. The primary indication for the JeRP system is an unstable fracture (Gehweiler type I/III) or/ and TAL injury (Dickman type II).