Computing the Radar Cross-Section (RCS) of a given object is a topic of major importance for many applications, e.g., target detection and stealth technology. In this context, high-frequency asymptotic methods are widely used. In this article, we derive a Gaussian Beam Summation (GBS) method for both metallic and dielectric targets. The basic idea is to use the GBS method to compute the scattering far fields generated by the equivalent currents flowing on the surfaces. The validity of the proposed method is then investigated in the X-band. To accomplish this, the results obtained using this technique were compared to those obtained using other sufficiently accurate methods such as the ray tracing of FEKO and the ray asymptotic solution. As an example of the method’s accuracy, the GBS method was used to obtain the wave field in a homogeneous medium by fitting the results to a point source. In the same way, the method was used to compute the RCS of dielectric cuboids.