PURPOSE: To investigate the effect of fibular malreduction on ankle joint after tibia interlocking IM nailing of tibial and fibular fractures according to type of fibular fractures at preoperation. MATERIALS AND METHODS: Thirty-nine patients who had ipsilateral tibiofibular fracture were analyzed clinically and radiographically. The talocrural angle and the distance from joint line to the tip of fibular were measured on both ankle standing AP view. The difference of angle and distance of both ankle were analyzed by paired t-test and correlation between defference and AOFAS score by Spearman correlation coefficients. RESULTS: The difference of The talocrural angle and the distance from joint line to the tip of fibular of both ankle was statistically significant (p<0.05). The correlation between this difference and AOFAS score was statistically insignificant (p>0.05). CONCLUSION: In tibia interlocking IM nailing of tibia and fibula fracture, malreduction of fibula could cause the change of ankle joint.