The present invention provides an SPR sensor cell and SPR sensor with extremely good detection sensitivity. This SPR sensor cell is provided with: an underclad layer; a core layer, at least a portion of which adjoins the underclad layer; and a metal layer covering the core layer. The core layer is configured from a uniform layer and a gradient layer disposed between the uniform layer and the underclad layer. The refractive index NCO of the uniform layer satisfies the relationship 1.34 <= NCO < 1.44. The refractive index NCL of the underclad layer and the refractive index NCO of the uniform layer satisfy the relationship NCO - NCL >= 0.020. The refractive index of the gradient layer in the thickness direction from the underclad layer side towards the uniform layer side exceeds NCL and gradually increases in the range below NCO.