We propose a novel solid-state electrical ammonia sensor based on a vertical organic diode with high-density nanopores in the top electrode. The proposed ammonia sensor has a detection limit of 20 ppb, a real-time response, sufficient selectivity, simple structure, high reproducibility, and a low production cost. In addition, we used the proposed sensor to detect the nasal breath of rats directly. After controlling the relative humidity and filtering out the CO
, we successfully obtained repeated real-time, reliable responses. This is the first demonstration of a solid-state sensor having reliable responses to the breath ammonia of an animal. The sensing response between normal and acute groups is significantly different (p < 0.05). These results demonstrated that the proposed ammonia sensor can detect liver that undergoes moderate hepatopathy.