We study the sensing properties of an intensity-modulated fiber-optic surface plasmon resonance (SPR) sensor using radially polarized beam (RPB). Because of the rotational symmetry of fiber and RPB, surface plasmon can be excited more efficiently at the sensor surface, which results in an obvious improvement of the sensitivity. Our experiments demonstrate that the sensitivity in the case of RPB illumination is three times higher than that of linearly polarized beam illumination.