Gas phase production of polyethylene (PE) results in a powder with particles of different sizes. This experimental work on the samples from an industrial reactor shows that there is a difference between Mw and properties of the PE particles as a function of their sizes. The results showed that for each type of polyethylene there is a critical particle size for which Mw reduces to a minimum. Particle size was found to have strong influence on the rheological behavior of high-density polyethylene (HDPE) homopolymer. The smallest homopolymer HDPE particles showed the highest Mw with distinctly different flow behavior. Differences in properties for HDPE copolymer and linear low density polyethylene (LLDPE) samples were less profound.