A low-cost imaging system is developed for mapping skin venous oxygen saturation. The system consists of a black-and-white CCD camera and cheap LED light sources working at 660 nm and 800 nm wavelength. With the two wavelength sources alternately illuminating the skin, the CCD camera collects images carrying signals of diffuse reflectance before and after the venous occlusion induced by a low cuff pressure. Using the Monte Carlo method, the relationship between the venous saturation value and the diffuse reflectance is determined. Therefore images captured can be converted into the venous saturation map. Experiments on human fingers and palm show that the measured data is in line with previous published data, demonstrating the effectiveness of the system on monitoring blood oxygenation in local tissues.