We treated 35 fractures of tibia by using Interlocking intramedullary nail from Nov. 1987 to Jan. 1990 and analysed the phenomena of angulation on distal part of inserted nails as shape of fracture and style of the nail. The level of the tibial shaft fracture was in proximal third of tibia in two cases, in middle third in thirty cases and in distal third in three cases. The shape of fracture were eight cases of transverse fracture, five of oblique, seven of spiral and fifteen of comminuted. The used nails had three variable style as clover leaf cross section (Grosse-Kempf type) in 24 cases, round (Russel-Taylor type) in nine and square (Brooker type) in two, all of them was gradully antecurved about 20°proximally to allow negotiation of the curve of upper third of tibia (Herzog's curve). Average period of follow-up was 18.2 months and all cases was obtained solid union. In twenty six cases, angulation was discovered at distal part of nail, which was pointed also to anteriorly. All cases of intact posterior wall of the tibial midshaft had developed angulation of distal part of nail posteriorly and average degree of angulation was 4.8°As style of nails, distal angulation was observed in Grosse-Kempf to average 5.4°, Russel-Taylor to 3.5°but two cases used Brooker nail was not angulated. The site of angulation was between 3.2cm and 8.5cm and average 4.5cm from distal tip of nail. During operation, separation of fracture fragments and breakage of cortex were happened in 6 cases, which had no relation to fracture healing time but static interlocking was needed.