Objective: To retrospectively analyze the effect of unilateral external fixators in the treatment of lower third humeral shaft fractures.Methods: From October 1997 to October 2003, 33 patients aged 15 -70 years (average 31 years) with lower third humeral shaft fractures were treated with unilateral external fixators. There were 9 spiral fractures (type A1), 1 oblique fracture (type A2), 3 transverses fractures (type A3) and 20 comminuted fractures (11 type B1, 9 type B2) according to AO classification. Fifteen cases were treated with open reduction and limited internal fixation and fixation with external fixators, 10 cases treated with open reduction and fixation with external fixators, and 8 cases treated with closed reduction and fixation with external fixators. Nerve exploration was undertaken in 9 cases with preoperative radial nerve injury. External fixators were removed after bone healing. The average follow-up was 18 months with a range from 8 to 24 months. Results: The time of bone healing ranged 11-22 weeks (average 14 weeks). The latest follow-up showed the functions of 9 cases of preoperative radial nerve injury and of 2 cases postoperative radial nerve injury and the function of elbow were recovered to normal. There were only 7 cases of superficial infection at pin hole, which was subsided by using oral antibiotics and pin-hole care with mild disinfectants.Conclusions: Fixation with unilateral external fixators combined with open reduction and limited internal fixation has a good effect in the treatment of lower third humeral shaft fractures.