Objective: Closed reduction and percutaneous fixation is known as the optional treatment for displaced supracondylar humerus fractures. The retrospective study is to compare external fixator versus K-wires to evaluate the clinical and radiological results for displaced supracondylar humerus fractures. Methods: Among all of 40 patients, there were 16 girls and 24 boys with the mean age of 7.26 years (range from 4 to 13 years). Closed reduction followed by percutaneous fixation of external fixator or K-wires were performed in our department. Medical records were reviewed to obtain demographic information as well as preoperative and postoperative clinical and radiological data regarding fracture type, displacement of fracture, neurovascular status, range of motion and infections. The Flynn's criteria et al. was used to evaluate the clinical outcomes. Results: There was no significant different in age, gender, affected sides, the type and displacement of fracture and nerve palsy between two group (P>0.05). According to the Flynn's criteria et al., two groups showed the similar to clinical outcome (P>0.05). Two (13.3%) children presented skin infection around screws, while five (20%) patients presented skin infection in K-wires, in which four (80%) patients develop the migration of K-wires. There was significant different in skin infection between two groups. Three (12%) patients presented ulnar nerve palsy in K-wires, while one (6.7%) patient presented radial nerve palsy in external fixator. Conclusion: The percutaneous K-wires or external fixator fixation following closed reduction is an effective method in the treatment of displaced supracondylar fractures of humerus. K-wires have the risk of ulnar nerve palsy and skin infection or the migration of wires. External fixator could facilitate to reduce the fracture by the direct manipulation of external fixing frame and provide the stabilization of fracture without the neurological risk to ulnar nerve.