Transmission light property due to surface plasmon resonance (SPR) was investigated for glass substrate/500-nm-thick fluoropolymer (CYTOP) with a grating structure/thin metal film/mixed solution of water and glycerol system. Transmission light peaks were observed due to grating-coupled SPR, with a remarkable peak intensity when pure water exists as an ambient dielectric. CYTOP exhibits a refractive index close to that of water, and the remarkable peak intensity was attributed to long-range SPR. The monitoring of polyelectrolyte layer-by-layer film deposition using transmission light was also investigated.