The microwave cavity perturbation method was applied for the measurement of the dielectric constants for polycrystalline samples of ten aromatic compounds (naphthalene, anthracene, phenanthrene, pyrene, chrysene, perylene, durene, acenaphthene, biphenyl, and p-terphenyl.) The method is shown to give a reasonable result, if the effect of the second order perturbation term is properly included and if Bottcher’s equation is carefully applied in transforming an apparent dielectric constant obtained on a powder sample into the mean dielectric constant of a crystal. The nature of the ordinarily used cavity perturbation equation and of Bottcher’s transformation equation is discussed in this respect. The obtained mean dielectric constants are; naphthalene 2.87, anthracene 3.12, phenanthrene 2.96, pyrene 3.14, chrysene 3.09, perylene 3.34, durene 2.55, acenaphthene 2.94, biphenyl 2.88, and p-terphenyl 2.98. The molecular polarization calculated from these values agreed quite well with the values estimated from the...