The reflection and transmission properties of inhomogeneous clouds (or ensembles of clouds) are simulated, which is relevant for e.g., satellite remote sensing and climate modeling. One of the main cloud properties is optical thickness. Here cloud inhomogeneity is assumed to arise from cloud optical thickness variability over a certain area. A simple triangular distribution function of cloud optical thickness is used, based on observations of cloud liquid water path distribution. An accurate plane-parallel radiative transfer model is employed to study the effect of cloud optical thickness variability on the reflection and transmission properties of inhomogeneous clouds. The effect of cloud sides is neglected. Results of the reflectivity, albedo, and transmission of inhomogeneous clouds are shown. Inhomogeneous clouds have lower reflectivity and albedo, and higher transmission than homogeneous clouds with the same number of cloud particles. The ratio of average cloud optical thickness to effective cloud optical thickness, which is the optical thickness of a homogeneous cloud that has the same reflection or transmission properties, is about 1.3 for thin clouds (average optical thickness 5), and about 1.6 for thick clouds (average optical thickness 50).