Hydrogen-atom tunneling from and to linear alkenes in organic matrices at 77 K has been studied for elucidating the effect of matrices on the rate of the tunneling. The rate of hydrogen-atom addition to the vinyl carbon of alkenes does not depend on the length of allyl chains bonded to the vinyl carbon, whereas the rate of hydrogen; atom abstraction by methyl radicals from the allylic carbon decreases with increasing length of alkyl chains bonded to the allylic carbon. These effects are explained as due to the resistance of matrices to the change of the C-C-C bond angle of the reacting carbon during the tunneling. For hydrogen-atom abstraction, the resistance causes the increase of the height of the potential barrier between the entrance and the exit of the tunneling channel, whereas the resistance does not cause the retardation of the tunneling to the vinyl carbon since the bond angle scarcely changes during the tunneling.