The fabrication of lead halide perovskites involves different types of organic solvents, which are not only harmful to the environment but also expensive. Herein, we present an ultimately green process to prepare CH₃NH₃PbBr₃ (MAPbBr₃) nanowires without using any organic solvents, acids, and alkalis. According to the formula of Pb(OH)Br, only PbBr₂ and water are used to synthesize Pb(OH)Br. Subsequently, the Pb(OH)Br nanowires are converted into MAPbBr₃ nanowires via a thermal evaporation technique (i.e., exposing Pb(OH)Br nanowires to MABr vapor). The prepared MAPbBr₃ nanowires show comparable optical properties to those prepared using organic solvents. Such an ultimately green fabrication method can alleviate the environmental concerns and reduce the cost of perovskite commercialization.