The purpose of this study was to evaluate the torque effect of orthodontic wires. Ten types of orthodontic wires (five types of materials, two types of cross-sectional dimensions) were selected. Each group of wire type was constituted with five specimens. These specimens were tested on the universal testing machine(Instron) with specially-designed jig. The torque-twist curve of each wire was obtained and the results were analyzed statistically. The results were as follows : 1. 0.017″ X 0.025″ wire showed more torque effect than 0.016″ X 0.022″ wire at the same twist. 2. Torque effect was the greatest in stainless steel and the least in Nitinol. 3. The maximum amount of torque was the greatest in heat-treated Blue Elgiloy and the least in Nitinol.