The ZnO nanorods-based ammonia (NH3) gas sensors with different electrode spacing are fabricated and studied. Experimentally, the hexagonal ZnO nanorods were prepared by a hydrothermal method. The diameter and length of ZnO nanorods were about 179±2, 1806±5 nm, respectively. By shrinking the electrode spacing, the sensor response of studied device is improved and the sensor response is enhanced more than ten times in magnitude. The improved NH3 sensing ability caused by shrink electrode spacing is attributed to the presence of more grain boundaries and depletion layers. Therefore, the studied device with the shrink of electrode spacing provides a promise for high-performance ammonia sensing applications.