In this paper, we present radio-frequency electro-magnetic field characterization of an electrooptic (EO) probe. This probe is able to simultaneously measure temperature and one component of the electric field (e-field) in a continuous wave (CW) or in a pulsed regime. For this purpose, linearity, selectivity, and sensitivity measurements are performed in air and in a cuvette filled with a water solution. The media are exposed to 1800-MHz CW electromagnetic wave through a transverse electromagnetic cell. Numerical characterization is also performed using finite-difference time-domain simulations. The EO probe presents a dynamic range exceeding 70 dB. Selectivity up to 25 dB is measured, demonstrating the ability of the EO probe to measure one unique component of the e-field. The EO probe sensitivity is equal to 0.77 and to 0.18 V * m-1Hz-½, in the air and in the water solution, respectively. This millimeter-sized EO probe is particularly suited for the measurement of ultrawide bandwidth and high-voltage e-fields up to a few megavolts per meter.