The present invention provides a surface plasmon resonance (SPR) sensor cell and SPR sensor having exceptional detection sensitivity. This SPR sensor cell has: an undercladding layer; a core layer disposed in such a manner that at least part of the core layer is adjacent to the undercladding layer; and a metal layer covering the core layer. The core layer includes a uniform refractive index layer and a graded refractive index layer. The graded refractive index layer is positioned between the uniform refractive index layer and the metal layer. The refractive index of the graded refractive index layer is greater than or equal to the refractive index of the uniform refractive index layer, and continually increases from the surface of the uniform refractive index layer-side to the metal layer side, in the thickness direction thereof.