A scintillator unit that can reduce crosstalk when the scintillator unit includes a plurality of scintillators and a radiation detector are provided. More specifically, a scintillator unit includes a reflective layer between a plurality of scintillators and the plurality of scintillators, wherein an adhesive layer and a low-refractive-index layer with a lower refractive index than the adhesive layer are located in this order on the scintillators between the scintillators and the reflective layer.