In this paper, a solid type pH sensor with ultra-low power consumption of 8.2 X 10-4 mAh for each measurement and ultra-high accuracy of 0.01pH was developed for real-time monitoring of cow-rumen. The sensor combines a metal-oxide-semiconductor field-effect transistor (MOSFET) with a separate gate as a sensing electrode, which was fabricated by indium tin oxide (ITO) with an optimized capture structure. The evaluation results revealed that the sensor has high-sensitivity of >14 μα/pH, while keeping a stable baseline at pH 7 in cow's rumen for several days. Fields test was carried out by using above sensor, which clearly demonstrated that the pH values strongly depend on activities of the cow recorded by a camera. The developed pH sensor is believed significant important for preventing diseases as well as for improving the efficiency of the food production.