The paper is devoted to the investigation of the accuracy of the Rozenberg approximation for the reflection function of a semi-infinite absorbing random media. We found that this approximation can be used at y < 0.5, where y = root(1 -omega(0))/(3(1 - g)). Here omega(0) is the single scattering albedo and g is the asymmetry parameter. We also propose the modified approximation, which can be used at least up to y = 1-2, depending on the observation geometry.