There are provided an SPR sensor cell and sensor, both having very excellent detection sensitivity. The SPR sensor cell includes: an under-cladding layer; a core layer, at least a part of the core layer being adjacent to the under-cladding layer; and a metal layer covering the core layer. The core layer includes a uniform layer and a gradient layer arranged between the uniform layer and the under-cladding layer; a refractive index NCO of the uniform layer satisfies a relationship of 1.34≦NCO