As an innovative optical method, the laser induced thermal grating technique has been used for the measurement of the thermophysical properties of working fulids. This measurement technique has been developed to determine thermophysical properties nuder special conditions, particularly in the fields related to high technology research and development. These special conditions include electrical conductivity, corrosiveness, toxicity and anisotropy of the sample, and extremely high or low temperatures and pressures. In the present paper, the authors interpreted in detail the principle, measuring technique and experimental apparatus for determining the thermal diffusivity of liquids using the lader induced thermal grating technique. Some typical measuring results were presented and compared with those from other sources.