Some kinds of pregraphitic carbons exhibit temperature-dependent negative magnetoresistance even at helium temperatures. To account for this anomalous behavior, two assumptions have been introduced. First the sample is composed of an assembly of many thin films which are nearly independent of each other elastically. Secondly, ionized impurity scattering makes an important contribution to the resistivity. Rayleigh waves with small damping and small sound velocity propagate through each film and the scattering due to the Rayleigh wave phonons gives rise to a carrier relaxation rate which decreases as the square of the thin film thickness. Since the screening length of an ionized impurity potential decreases with magnetic field, this process leads to a negative magnetoresistance. Combining these two effects, the qualitative features of the temperature dependent negative magnetoresistance can be explained within the framework of Brights Theory. Keywords Negative magnetoresistance, Pregraphitic carbons, Effect of Rayleigh waves, Negative magnetoresistance.