In this study, we experimentally confirmed the sensitivity enhancement by the nanowire-based surface plasmon resonance (SPR) sensor structure. Gold nanowire samples with a period of 500 nm were fabricated by interference lithography on a gold-SF10 glass substrate. Sensitivity enhancement compared to a conventional SPR structure was measured to be 31% when evaluated using a varied concentration of ethanol at a dielectric surrounding layer. This result is consistent with numerical data of rigorous coupled-wave analysis. Rough surfaces of thin gold film and gold nanowires are deemed to induce the sensitivity degradation by more than 10%. More significant sensitivity improvement can be achieved by implementing finer nanowires.