A new method for the determination of two characteristics of a sample of particles, the correlation of particle mass density with particle size and the distribution of particle mass density, is presented. The new method to meet these requirements is based on the combination of two optical particle sizing techniques where the measured particle characteristics have a different dependence on particle mass density. Photosedimentation and laser diffraction were chosen as suitable techniques for this goal. The determination of particle mass density by photosedimentation and laser diffraction is based on the fact that for each particle size class of the sample to be analysed the mass density can be calculated by an application of the Lambert-Beer law. The particle size distribution of the sample has to be known for the determination of particle mass density, and it is measured by laser diffraction. From this, two particle characteristics, the relationship of particle mass density and particle size and the distribution of particle mass density, are obtained. The capacity of the algorithm and its limitations are demonstrated by computational simulations including an error propagation analysis. Experimental results are shown for homogeneous and heterogeneous materials.