Objective To evaluate the result of treating nonunion of lower segment of humerus with combination of rib flaps of cross chest and double plates. Methods From Feburary 2000 to May 2006, 21 cases of nounion of lower segment of humerus were treated. There were 13 males and 8 females with an average age of 36.5 years (range, 17-56 years). Accordingto AO classification, there were 5 cases of type A1.3, 7 cases of type B1.3, 6 cases of type B2.3, 2 cases of type B3.3, and 1 case of type C1.3. All nonunion occurred after internal fixation, which was caused by bone resorption at fracture end in 12 cases, by plates breakage in 3 cases, and by internal fixation loosening in 6 cases; including 8 cases of hypertrophic nonunion and 13 cases of atrophy nonunion without pseudoarthrosis. An average time of nonunion was 1.5 years (from 8 months to 3 years). All cases were treated with combination of rib flaps of cross chest (length, 3.0-3.5 cm) and double plates. The pedicle was divided 8 to 10 weeks after operation and all cases carried out functional exercise. Results The patients were followed up for an average time of 18.2 months (range, 1-3 years). All nounion of lower segment of humerus were healed and no radial nerve injury occurred. Primary heal ing of wound was achieved at both donor and recipient sites. Bony union was achieved in all cases after an average time of 3.5 months (range, 3-5 months) after operation. According to the the Hospital for Special Surgery (HSS) functional elbow index, the average score was 89.3 (range, 81.7-92.5) and the outcome was excellent in 14 cases, good in 4 cases, and poor in 3 cases, the excellent and good rate was 85.7%. Conclusion Combination of rib flaps of cross chest and double plates is an effective method of treating nonunion of lower segment of humerus.