Abstract: The research included the study of the spectral properties of Rhodamine C dissolved in 1-butanol in different concentrations (7*10–6, 1*10–5, 3*10–5, 5*10–5, 7*10–5 mol/L) at ambient temperature and studies its nonlinear properties with the calculation of some parameter like "Nonlinear refractive index" and the "Nonlinear absorption coefficient" in addition to select one of these concentrations (7*10–6 mol/L) to study the effect of changing the pinhole diameter on some of these parameter.