WO3 nanoparticles were generated by gas deposition. Deposits on Al substrates were studied by scanning force microscopy operated in the intermittent-contact (tapping) mode. At low surface coverage (< 0.5 %), we observed single nanoparticles with a mean size of ~ 1.5 nm. An increase of the amount of particles led to agglomerates, which appeared at surface coverages as low as 2 to 4 %. At full coverage the mean agglomerate size was ~ 5 nm. This value did not change as the sample was annealed at temperatures up to 250 °C. The size distribution of the agglomerates was found to be log-normal, i.e., similar to the size distribution of the gas-phase nanoparticles forming the deposit. For explaining the obtained log-normal size distribution of the agglomerates simulations of the agglomeration process were also carried out.