The characteristics of microwave reflectometry as a non-invasive device to examine the density distribution of inhomogeneous media using the technology of FM radar is presented. The microwave reflectometry system requires an optimized system hardware and the understanding of system response from the density distribution in order to provide the system solution to describe the object under test quantitatively. Among the applications, the use of microwave reflectomeoy in the area of applied plasma physics has been newly proposed and the number of usage is found to be increasing gradually. The microwave reflectometry systems that depend on the nature of the object under test are described. The experimental method to characterize the system is explained and the experimental results on the wavenumber dependence and the sensitivity on density perturbation are presented as well as the comparison to the results from the one dimensional numerical simulations.