The propagation characteristics of flattened Gaussian beams (FGBs) and super-Gaussian beams (SGBs) have been studied and compared with each other. Numerical illustrative examples have been given. The main result obtained in this paper is that the FGB and SGB with the same M2 factor and beam width demonstrate the very similar propagation and transformation characteristics, including the intensity distribution and diffraction effect due to the aperture, while they propagate through an optical system.