The damages created on the sensitive devices of satellites caused by the trapped energetic particles, due to cosmic and solar radiations in the magnetic field of the earth, are significant. In order to prevent these damages, the sensitive devices are covered by shield elements. The elements, depending on their atomic number (Z-value) have different effects against nuclear radiations. So the best shield is a composition of heavy and light elements. In this research, the simulation of the radiation shield is done by the MCNPX code for the sensitive devices of a satellite at distance of 700 kilometers and inclination of 60 ? , and the genetic algorithms is written in MATLAB software to determine an optimum shield for sensitive devices on the satellite. The algorithm written in MATLAB software was then linked with the MCNPX code, and an optimum shield composed of heavy and light elements was designed according to the volume and weight parameters of the shield.