A film containing three dimensional Bi2S3 nanowires network was obtained using Bi(NO3)(3) and thioacetamide as starting materials through three steps, namely the chemical synthesis of Bi2S3, preparation of its sol under ultrasonic condition and crystal self-assembly at 25 degrees C. The nanowires had diameters of 20-100 nm. The formation mechanism of the 3D nanowires network is the anisotropic growth of Bi2S3. The sensor based on 3D Bi2S3 nanowires network with an excellent response to ammonia at 30 degrees C. The response mechanism of the sensor for ammonia is a weak coordination adsorption of ammonia molecule on the Bi2S3 nanowires and the electron is partially transferred from ammonia molecule to bismuth (III) ion. The maximum response of the sensor to ammonia was up to 82.3 and had a good linear range from 30 to 350 ppm concentration, indicating its potential applications in the determination and leak alarm of ammonia.