Disclosed are a method of preparing a zeolite nanosheet and a zeolite nanosheet particle prepared thereby, and more particularly a method of preparing a zeolite nanosheet capable of preparing a monolayer zeolite nanosheet through a simple process of mixing a multilayer zeolite precursor with a swelling agent to swell the multilayer zeolite precursor and drying and calcining the multilayer zeolite precursor, wherein the monolayer zeolite nanosheet is useful to separate a catalyst or gas, and a zeolite nanosheet particle prepared thereby.