The hydrogen isotope composition of n-C15 to n-C32 n-alkanes was measured by GC-IRMS to investigate the behavior of H isotopes during evaporation. The H isotope fractionation of n-C15 to n-C19 ranged from -8.5 to -22.5‰, demonstrating the preferential vaporization of the isotopically heavier organic compounds. The H isotope fractionation rates of n-C16 to n-C18 showed no obvious fluctuations with time (average rates were 1.1, 0.5 and 0.3‰ per day, respectively); this indicated that fractionation followed the Rayleigh model. Although less conclusive, the fractionation of H isotopes in n-C19 also apparently followed the Rayleigh trend. Information on fractionation rates may be useful for identifying the dominant attenuation and degradation processes for organic substances in the environment. The results also highlight potential applications of isotope fractionation factors, which were determined by regression analysis, for investigations into the behavior of organic substances in the environment.