By using the femtosecond two photon photoemission technique, we directly measured the lifetimes of photoexcited electrons in two layered materials, graphite and SnS2. The inverse lifetimes of photoexcited electrons in these two-dimensional layered materials exhibit linear energy dependence, i.e., 1/tau proportional to(E-E-F), instead of quadratic, i.e., l/tau proportional to(E-E-F)(2) as predicted by Fermi liquid theory. This can be explained with the layered electron gas theory, according to which the electron-plasmon interaction is strong, even for electrons at low excitation energies, due to the formation of plasmon band in layered electron systems. Furthermore, our observations in SnS2 also suggest that in layered semiconductors, photogenerated electron-hole pairs will recombine directly by emitting plasmons, and this causes the lifetimes of the conduction band electrons to be much shorter than those in three-dimensional semiconductors.