An optical vector analyzer assisted by stimulated Brillouin scattering (SBS) processing is proposed and experimentally demonstrated. Benefitting from the selective amplification and attenuation achieved by the SBS processing, the proposed OVA has enhanced dynamic range and measurement accuracy. An electro-optic modulator produces an intensity-modulated optical double-sideband (ODSB) signal. During the SBS processing, the +1st-order sideband of the ODSB signal is amplified while the -1st-order sideband is attenuated. Thus, an optical single-sideband signal owning a large sideband suppression ratio is achieved, which is then served as the probe signal and passes through an optical device-under-test. Then, by square-law detection, a photocurrent carrying the frequency responses is generated. Receiving and detecting the photocurrent, the multi-dimensional frequency responses, including magnitude, delay, and phase responses, are obtained. In an experiment, 34.05 dB amplification and 22.85 dB attenuation are achieved by the SBS processing. A dynamic range enhancement of 14.01 dB is obtained by measuring an optical bandpass filter, which is well coincident with the theoretical result. The comparative optical transfer delay measurement of a high-precision variable optical delay line indicates accuracy improvement.