Abstract: Rotational relaxation of CS₂, in argon free jet was studied using laser-induced florescence （LIF）excitation spectrum of the R³B₂（150）X¹∑_g⁺ （0, 0, 0）band in the range of 352.4-352.7nm. The rotational temperatures T_r were derived from the LIF spectra detcected at 19 different points along the jet axis from X/D =3 to 15. Then the variation of T_r with the transitional temperature T was obtained. Based on the relaxation equation, the relationship between the rotation-translation relaxation probability P_R-T and T was derived. The result shows that in the range of low T, P_R-T probability increases with the decreasing of T, indicating that the attracting force between CS₂ and Ar plays a major role in the relaxation process.