An application of a small air-spaced coaxially fed rectangular microstrip patch antenna as a sensor for permittivity measurement is presented. The models used for the calculation of the permittivity from the shift in the resonant frequency for solid and liquid materials are described. The models are experimentally verified by measurements for several liquid and solid samples. The results are compared with those obtained using standard techniques, namely, coaxial probe and waveguide cell measurements. An error correction technique for the elimination of the systematic error of the measurement is also included.