An encapsulation of backside illumination photosensitive device including a circuit sub-mount, a backside illumination photosensitive device, a plurality of conductive terminals, and a heat dissipation structure is provided. The backside illumination photosensitive device includes an interconnection layer and a photosensitive device array, wherein the interconnection layer is located on the circuit sub-mount, and between the photosensitive device array and the circuit sub-mount. The conductive terminals are located between the interconnection layer and the circuit sub-mount to electrically connect the interconnection layer and the circuit sub-mount. The heat dissipation structure is located under the interconnection layer, and the heat dissipation structure and the photosensitive device array are respectively located at two opposite sides of the interconnection layer.