An image sensor module includes a circuit board, an image sensor package and an optical system. The circuit board has an upper surface and a lower surface, the substrate having a window. The image sensor package includes a mounting substrate and an image sensor chip mounted on the mounting substrate, the image sensor package being adhered to the lower surface of the circuit board such that the image sensor chip is exposed through the window. The optical system is provided on the upper surface of the circuit board to guide light from an object to the image sensor chip.