Using Fourier transform infrared spectrometry, the intrinsic diffusion coefficients of benzene, toluene, ethylbenzene, m-xylene, and o-xylene in H-ZSM-5, H-Beta, and H-MCM-22 were measured at different temperatures. By means of a microscopic model to describe the molecular diffusion in zeolites and the use of the transient state theory, the self-diffusion coefficients of molecules in zeolites with straight channels were calculated. The experimental results obtained are compared with those calculated theoretically, and they are discussed on the basis of the framework structure of the studied zeolites.