A novel NO2 gas sensing material based on metal-thiourea complex was greenly synthesized via facile mixing of CuCl2 and thiourea aqueous solution. Its synthesis has advantages, like no need of surfactants, noble metals or other toxic solvents, not necessarily to perform calcination process, thus less time consumed and easy operation. The gas sensing properties of the complex nanowires were investigated to detect NO2. The material showed a selective response to NO2 with a good linear relationship as the concentration of NO2 varies from 1 to 10ppm. Compared with different materials, the complex sensor exhibited rapid response with the response/recovery time of 150/200s even for 100ppb NO2 at 60°C. The reason of the enhanced gas sensing performances by the complex nanowires and the underlying mechanism of the special interaction of the host material (metal-thiourea complex) and the guest molecule (NO2) were studied.