Example embodiments relate to a method of manufacturing amorphous NiO thin films and nonvolatile memory devices including amorphous thin films that use a resistance material. Other example embodiments relate to a method of manufacturing amorphous NiO thin films having improved switching and resistance characteristics by reducing a leakage current and non-volatile memory devices using an amorphous NiO thin film. Provided is a method of manufacturing an amorphous NiO thin film having improved switching behavior by reducing leakage current and improving resistance characteristics. The method may include preparing a substrate in a vacuum chamber, preparing a nickel precursor material, preparing a source gas by vaporizing the nickel precursor material, preparing a reaction gas, preparing a purge gas and forming a monolayer NiO thin film on the substrate by performing one cycle of sequentially supplying the source gas, the purge gas, the reaction gas and the purge gas into the vacuum chamber.