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In this paper, we report on a free-space microwave system developed for the measurement of the relative complex permittivity of granular materials (wheat, soybeans and corn) and of pulverized materials (coal). The system consists of a transmitting antenna and a receiving antenna separated by a space filled by the sample to be characterized and a network analyzer for transmission measurement. The receiving antenna is mounted on a movable plate, which gives the flexibility of having different sample thicknesses. The system is considered a two-port device. The testing procedure developed is nondestructive and easy for implementation. At a fixed moisture level, the dielectric constant and loss factor of the test materials are determined and compared with other published data.