The mechanical stiffness of 4 configurations of the Translucent Hexagonal External Fixator(THEF) was analyzed and compared with conventional Ilizarov system in vitro. The advantage of the THEF was that it is less expensive, radio-translucent because it was made of carbon fiberepoxy. Stiffness in axial compression, torsion, A-P bending and lateral bending were measured in both fixators. The fixators were assembled into 90-90 and 45-135 configurations, respectively. In each configurations, two types of pin, smooth pins and olive pins, were used for transfixion. As compared with the Ilizarov fixator, the THEF was less stiff in axial compression when the two smooth pins were used for transfixion regardless of configuration, but was also less stiff in A-P and lateral bending except A-P bending when the smooth wires were assembled in 90-90 configuration, and lateral bending when the olive wires were assembled in 45-135 configuration. However, the THEF was more stiff in torsion regardless of configuration and type of wires used. When the olive wires were used, the THEF was more stiff than the Ilizarov fixator regardless of wire configuration in all loadiilg mode except AP bending. Changing the pin configuration from 90-90 to 45-135 decreased all stiffness of the Ilizarov fixator. However, lateral bending and axial compression stiffness with smooth wire and A-P bending stiffness regardless of types of wires were decreased in the THEF. Changing the smooth wires to olive wires increased the A-P and lateral bending stiffness in the Ilizarov fixator, while it increased all stiffnesses in the THEF. We believe that the results originated from the weakness of the material used. THEF may be an effective alternative for osteosynthesis, deformity correction in complex construct because of its radiolucency in spite of less favorable biomechanical properties in some loading mode.