A hydraulic hinge for a glass door has a fixing plate, a base, a pivot, a buffer module, and a clamping module. The base is combined with the fixing plate and has an oil passage. The oil passage is formed in the base. The pivot is rotatably mounted in the base and has an adjusting space communicating with the oil passage. The oil passage and the adjusting space are filled with oil. The buffer module is mounted in the base and has a sliding tube abutting the pivot. The clamping module is pivotally mounted on the pivot and can clamp a glass door. The glass door can be pivoted relative to the base. With the buffer module and the oil in the oil passage, the glass door can be closed in a smooth movement.