Ammonia is one of the most common chemical gases used in people’s daily life and industrial production. High concentration of ammonia can be harmful to both human and environment. The current research status of ammonia gas-sensitive materials is introduced in terms of metal oxides, conducting polymers, carbon nanomaterials, and other materials, while the characteristics of different gas-sensitive materials are analyzed. Then the applications of ammonia sensors in atmospheric environment, livestock breeding, food safety, and healthcare are discussed. The future ammonia sensors will be developed toward the direction of miniaturization and intelligence.