A film of benzenesulfonamide azo dye has been prepared by spray pyrolysis method onto BK7 glass substrate with average thickness of 2.7μm. This azo dye was derived from sulfamethoxazole and chromotropic acid by the Fox method. The optical constants (refractive index, n, extinction coefficient, k, dielectric constant, ɛ, optical, σopt, and electrical, σe, conductivities) were calculated for azo dye film by using spectrophotometer measurements of the absorption, transmittance and reflectance at normal incidence in the spectral range 300–900nm. Third order nonlinear properties has been characterized by calculating the effective thermal nonlinear refractive index, n2, and thermo-optic coefficient, dn/dT, of the azo dye solution using thermal lens technique. Furthermore, the thermal lens effect was utilized to demonstrate all optical switching for the sample solution.