A package structure of an image sensor is characterized in that an image sensing chip is directly packaged on a flexible circuit board by way of flip chip bonding. The package structure of an image sensor includes an image sensing chip, a flexible circuit board, and a transparent layer. A plurality of electrical circuits are formed on the image sensing chip. Each of the electrical circuits is formed with bonding pads. A flexible circuit board has an upper surface and a lower surface. Signal input terminals are formed on the lower surface and at positions corresponding to each of the bonding pads of the image sensing chip, respectively, for electrically connecting to the corresponding bonding pads of the image sensing chip. The signal input terminals are electrically connected to signal output terminals, respectively, for electrically connecting to the printed circuit board. The transparent layer is used for covering the upper surface of the flexible circuit board. The image sensing chip receives image signals via the transparent layer, transforms the image signals into electrical signals, and transmits the electrical signals from the flexible circuit board to the printed circuit board.