Objective To analyze the causes and managing methods of long bone fracture nonunion after allogeneic bone transplantation. Methods From December 1995 to December 2000, 43 cases of postoperative nonunion of long bone fracture were treated. These cases included 31 males and 12 females at the age of 19-57 years (40 years on average). The locations were femur in 11 cases, tibia in 21 cases, humerus in 8 cases and forearm in 3 cases. Bone nonunionafter allogeneic bone transplantation was caused by extensive soft tissue contusion and poor cover around bone fractue site in 6 cases, by incomplete debridement in 8 cases of osteomyel itis (including 6 without continual lavage and 4 only skin flap transfer), by secondary infection of wounds in 3 cases, by severe primary injury or secondary scar covering bone in 12 cases, instable internal fixation in 7 cases, and by earl ier weight bearing in 7 cases. Accroding to Weber classification, there were 4 cases of hypertrophic type and 39 cases of atrophic type. Basing on the type of nonunion, the methods such as refixation, bone retransplantation and transferring tissue flap were chosen to manage the cases. Results Incision healed by first intention in 37 cases, superficial infection occurred and cured after 2 weeks of dressing change in 5 cases, and sinus formed and cured after 2 months of dressing change and drainage in 1 case. All transferring tissue flap survived, and partial necrosis occurred at flap edge in 4 cases and cured after dressing change. All patients were followed up for 38-91 months with an average of 54.6 months. All the nonunion cases achieved bone union 5-11 months with an average of 7.6 months. But low extreme shorten monstrosity occured in 4 cases, malunion in 2 cases, functional l imitation near joints in 7 cases, and rotational l imitation of forearm in 1 case. Conclusion Fracture nonunion after allogeneic bone transplantation mainly shows atrophic type with overall or partial absorption of the allograft bone. The preconditions to guarantee fracture nonunion heal ing include stabil ity of fracture fixation, using transferring tissue flaps, controll ing infection, and adequate bone transplantion.