The reaction of the solid thin film of propene (C3H6) deposited on the silicon substrate at 10 K with cold H atoms (similar to27 K) sprayed over the solid films was studied. Propane and 2-methylpentane were found to be the major and minor reaction products, respectively. The rate for the formation of C3H8 increased steeply with a decrease of temperature from 35 to 10 K. This is the general trend for the low-temperature tunneling reactions investigated in our laboratory. With an increase of temperature from 40 to 55 K, the yield of C3H8 showed a slow increase. This may be due to the replenishment of the reactant C3H6 molecules to the surface above similar to40 K (i.e., solid-phase diffusion). The yield of C3H8 from C3H6 was lower than that of C2H6 from C2H4. This may be due either to the hindrance of the proximity approach of the H atom to the C3H6 double bond by the presence of the methyl group and/or to the annihilation of the H atoms by the H-atom abstraction reaction with the reaction product C3H8 to form the s-C3H7 radical on the surface of the solid film.