The properties of Modified Laguerre-Gaussian beams (MLGBs) propagating through a fractional Fourier transform (FRFT) optical system are investigated. The analytical transformation formula for MLGBs propagation through an FRFT optical system is derived based on definition of the FRFT in the cylindrical coordinate system. By using the derived formula, the normalized intensity distribution of MLGBs in the FRFT plane is graphically illustrated with numerical examples, and the influence of different parameters on the normalized intensity distribution is discussed.