The weak X-ray capture capability of organic scintillators always leads to poor imaging resolution and detection sensitivity. Here, we realize an efficient and reabsorption-free organic scintillator at the interface of perovskite nanosheets using a very efficient energy transfer strategy. Our steady-state and ultrafast time-resolved experiments supported by density functional theory calculations demonstrate that an efficient interfacial energy transfer from the perovskite nanosheet to the organic chromophore with thermally activated delayed fluorescence (TADF) character can be achieved. Interestingly, we found that the direct harnessing of both singlet and triplet excitons of the TADF chromophores also contributed greatly to its remarkably enhanced radioluminescence intensity and X-ray sensitivity. A high X-ray imaging resolution of 135 μm and a low detection limit of 38.7 nGy/s were achieved in the fabricated X-ray imaging scintillator.