External fixation systems are frequently used to correct defects in the human skeletal system using bone transport. Composite materials such as fiber-reinforced polymers (FRP) have been increasingly used for bone transport fixators since they have low density and are translucent to X rays. However, the mechanical analysis of FRP rails is complex since the material is anisotropic and heterogeneous. Static finite element analyses of two carbon-fiber reinforced rails were developed using a commercial software (ANSYS 15.0, ACP Pre-Post components) to predict the rail stiffness, which is an important property to ensure the correct alignment of the segments during the orthopedic treatment. Numerical models yielded differences in stiffness under two bending modes between 1% and 15%; and a difference of 50% for torsion load. The developed rails showed a similar or even higher stiffness than commercially available rails. Thus, the design of composite materials for orthopedic devices aided by numerical modeling tools is a viable process that can be implemented in our country.