Purpose: The aim of the study was to investigate the therapeutic effect of fibula derotation osteotomy for post-traumatic malunion of the lateral malleolus. Method: The analysis was performed on 37 patients with lateral malleolus malunion combining traumatic arthritis. All the patients aged from 15 to 63 years (male: female ratio, 26:11) and were treated in our hospital from Oct.2005 to Jan. 2009. They complained of persistent pain, joint swelling, limp and restricted daily activities. Lengthening and derotating transverse or Z-osteotomy with bone graft and internal fixation as operative intervention was adopted. The outcomes of all patients were assessed by clinical examination, AOFAS ankle hind foot score and plain radiographs. Result: Fibular length and restoration of the ankle mortise was successful in all the cases. There were no significant infections, neurologic complications, nonunions or compartment syndromes as a result of the osteotomy. Patients were followed up for an average period of 29 (range, 12 to 45) months after the surgery. All patients showed radiological evidence of bony union on followup. The post operation average AOFAS score was 84 (pain: 32, function: 42, and alignment: 10) which was much higher than 31 before operation.Conclusion: Fibula derotation osteotomy provides the treatment of ankle fractures which induced by lateral malleolar injury or lateral malleolus malunion, with successful clinical efficacy at short term.