Abstract: Experimental investigation of Stimulated Brillouin Scattering (SBS) in SF. gas of lower pressure pumped by KrF laser with bandwidth of 0.5cm^-1 and pulse duration of 23ns (FWHM) were reported. Experimental measurements were performed on SBS reflectivity versus pump energy, gas pressure and focal length. The effects of gas pressure and Rayleigh range on SBS threshold were discussed.