Abstract: Current interest in the molecular mechanism of gene engineering places great importance on the structural probing of nucleic acids . In this paper preliminary study on the structure of uracil , a base residue of RNA , in aqueous solu -tions of different pH values by coherent anti - Stokes Raman scattering (CARS) is reported .The results obtained reveal Raman lines associated with the stretching and bending vibration modes of the uracil ring around 1 000 cm-1. It is also found that these Raman lines are sensitive to pH of the solutions used . All these findings , however , are difficult to be observed by laser resonance Raman spectrosccpy which is used widely in practice at present .Therefore , we conclude that CARS measurement seems to be a powerful tool capable of offering structural specificity associated with molecular vibrational frequencies of base residues of nucleic acids and their interaction with the surrounding media . In addition to a significant suppression of interference from fluorescence either intrinsic to the sample or caused by impurities , this approach is expected to be able to provide structural information of transient species during relavant molecular processes .