Thermal rebound of nanoparticles on the surface of fibers is of big concern in collecting nanoparticles. Another factor influencing the collection of nanoparticles is the inhomogeneity of fiber packing. The present work studied the influence of filter inhomogeneity on the collection efficiency of nanoparticles by using wire screens as uniform structure in comparison to real filters. As a result, the single fiber collection efficiencies of nanoparticles through wire screens are in good agreement with those predicted by Kirsch and Fuchs (ηD = 2.7Pe-2/3), but the dependence of real filters on Pe is somewhat smaller than –2/3 and in agreement with (ηD = 0.84Pe-0.43, Wang et al., 2007). The dependence of single fiber collection efficiency on Pe for the real filters is well explained by considering non-uniformly packed filter consisting of two regions of densely packed and loosely packed fibers.