A molecular Filtered Rayleigh Scattering (FRS) diagnostic system was demonstrated to measure thermodynamic properties in combustion environments. The diagnostics system was composed of a narrow line width laser, a molecular/atomic absorption filter and a collection device such as ICCD. The absorption filter was used to modify the spectra of the Rayleigh scattering signal from the flow field illuminated by a laser sheet from a Nd:YAG pulsed laser. The laser was tuned to an absorption line of iodine vapor contained in the filter. This caused Mie scattering and background scattering from solid particles and strong absorption on the surface while much of Doppler broadened Rayleigh scattering was transmitted through the filter. The thermodynamic parameters were deduced from the measured transmission of the molecular Rayleigh scattering. The FRS diagnostic system and the iodine filter cell were described. On the basis of diagnosing FRS image and measuring iodine vapor absorption spectrum, the 2D temperature and density fields of methane/air premixed flame were obtained. The measured density at 15 mm above the burner surface is 0.19 kg/m3, and temperature is (1 827±84) K, which is good agreement with the results measured by using CARS method in the same condition. The uncertainty of temperature measurement by FRS is less than 8%. Furthermore, FRS technique was used to diagnose the atomization steam and supersonic exhaust flows. The results turbulence structures on the area of laser action were obtained. These demonstrate the abilities of the FRS technique to measure temperature and density fields and to enhance flow visualization in a combustion environment.