Reflection spectroscopy was applied to evaluate the optical homogeneity and the refractive index of thin porous silicon (PS) layer. Variation in PS layer optical thickness was evaluated by measuring and mapping the reflectance over the surface area. For the circular anodization area of 17 mm diameter, the measured variation was less than 5 % on an area of 11 mm diameter. The anodization electrode position was found to have little influence on the homogeneity. A method to derive refractive index from a reflection spectrum is studied. The wavelength dependence of PS index measured by the method showed fair coincidence with the calculation based on effective medium approximation. In the two layer PS formation, optical thickness was found to change whether high porosity or low porosity layer is formed first.