The diffusion coefficients of isopentane (i-C5H12), 1-hexene (C6H12), cyclohexane (C6H14) in polyethylene particles were measured by a highly sensible microbalanceintelligent gravimetric analyzer, using the desorption method with N-2 as a bypassing gas. Both the effective diffusion coefficients (D-eff) and dilute diffusion coefficients (D-eff(similar to)) were measured simultaneously. It was found that D-eff(similar to) was about one magnitude smaller than D-eff and the logarithmic form of D-eff(similar to) was linear with that of D-eff. In addition, the effects of particle size and distribution, polymer properties (e.g., the crystallinity and melt index), and operating conditions (e.g., temperature and pressure) on D-eff were systematically investigated. The results showed that Deff increased linearly with the increase of the square of particle size. The diffusion behaviors of hydrocarbons in polyethylene are of great importance in the polymerization and purging processes. (C) 2010 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013