Nano-filled polyurethane coatings were prepared by incorporation of various amounts of untreated and amino propyltrimethoxy silane (APS) treated TiO2 nanoparticles. TEM and AFM techniques were employed to evaluate dispersion of nanoparticles and surface morphology of the coating, respectively. TEM observations revealed that the APS treated nanoparticles have a better dispersion and smaller agglomeration, compared with their untreated counterparts. AFM images revealed that, surface roughness of the coatings increased with increasing of nanoparticles content, however, at equal level of loadings; coatings containing untreated nanoparticles showed a higher surface roughness. Colour changes (colour coordinates data measurements), mechanical properties and surface morphology of the PU nanocomposite coatings, before and after being exposed to a QUV chamber for 1000 h were studied using various techniques. The results revealed that addition of 0.5 to 1.0 wt.% APS treated TiO2 nanoparticles reduces photocatalytic activity, and improves the weathering performance PU nanocomposite coatings. Tensile strength measurements showed significant improvement of mechanical properties of PU coatings containing modified TiO2 nanoparticles. Results also revealed that the colour measurement is a useful technique and non destructive method for evaluation of coating's performance against weathering conditions. The experimental results showed a good correlation between different techniques findings. (C) 2010 Elsevier B.V. All rights reserved.