Objective To investigate the functional outcomes of buttress plate fixation and simple screws fixation for the treatment of supination-adduction type-II medial malleolar fractures so as to provide reference for selection of internal fixation. Methods Between March 2009 and December 2012, 53 patients with supination-adduction type-II medial malleolar fractures were treated with open reduction and internal fixation. Of them, buttress plate fixation was used in 30 cases (buttress plate fixation group), and screws fixation was used in 23 cases (screw fixation group). There was no significant difference in age, gender, injury cause, injury side, disease duration, and combined injuries between 2 groups (P>0.05). Complications and full weight-bearing time were recorded; the American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score and the visual analogue scale (VAS) were used to evaluate the functional outcomes. Post-operative anteroposterior and lateral X-ray films were taken to evaluate fracture reduction and union condition. And the treatment failures were recorded. Results There was no significant difference in incision related complication rate and infection rate between 2 groups (P>0.05). The patients were followed up 46-91 months (mean, 64.5 months) in buttress plate fixation group and 44-86 months (mean, 59.5 months) in screw fixation group. The full weight-bearing time of the buttress plate fixation group was significantly shorter than that of screw fixation group (t=2.05,P=0.04). During follow-up time, malunion and nonunion occurred in 2 cases and 1 case of screw fixation group; anatomic reduction and bony union were observed in the other patients of 2 groups. The union time showed no significant difference between 2 groups (t=1.06,P=0.30). No significant difference was found in AOFAS score and good and excellent rate, VAS score, operation failure rate, and traumatic osteoarthritis rate between groups (P>0.05). Conclusion For patients with supination-adduction type-II medial malleolar fracture, the angle between fracture line and tibial axial line is too small to be fixed firmly with simple screws fixation, with a relatively higher failure rate. And buttress plate fixation can reach rigid fixation, and has better functional outcomes.