Surface plasmon resonance sensor based on resonant interaction between a guided mode of a single-mode optical fiber and a surface plasmon wave supported by a thin metal overlayer is presented. Two modes of operation of the sensor based on the measurement of changes in the fiber mode attenuation and on the measurement of changes in the wavelength at which the resonance occurs are described. Theoretical analysis of the proposed sensing structure based on the equivalent planar waveguide approach and the mode expansion and propagation method is carried out. It is shown that the operation range of the sensor may be tuned by a thin dielectric overlayer. Experimental results have shown that in both the modes of operation the sensor is capable of detecting changes in the refractive index of the sensed medium below 2 multiplied by 10-5.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.