The mean size of colloidal lead sulfide particles in nanocomposites with organic materials was varied from 4 to 80 nm by addition of sodium dodecyl sulfate or acetic acid. The refractive index and absorption coefficients of the resulting nanocomposites were measured at 632.8 and 1295 nm. The refractive index of the resulting nanocomposites was In the range 1.7-3.9 and belongs, therefore, to the highest values reported for such systems. The refractive indices and absorption coefficients of the nanocomposite decrease continuously when the particle diameters are below ca. 25 nm. For particles with average diameters above ca. 25 nm, the extrapolated refractive index of the PbS particles is in good agreement with that of bulk PbS (4.3), but the values drop for smaller particle diameters, e.g., to 2 for mean particle diameters of 4 nm.