Optical properties of iron pillared clays (Fe-PILCs) were determined by using spectrophotometer measurements coupled with the solution of the radiative transfer equation (RTE). The specific absorption and scattering coefficients, as well as the phase function for scattering, were obtained as a function of the wavelength in the range from 300 to 500 nm. Optical properties of the Fe-PILCs are greatly affected by their iron contents which are ascribed to changes in their textural properties and are significantly different from those of two other iron containing materials, goethite and zerovalent iron. To show an application of the optical properties, the quantum efficiency of the heterogeneous photo-Fenton process with a Fe-PILC was determined. The results indicate that Fe-PILCs could be used as catalysts in large-scale photoreactors whose dimensions could be adjusted in a wide range according to the catalyst load and iron content to be used.