Provided are a nano-sized thin sheet-like pseudoboehmite and a method of producing the same. The method of producing a sheet-like pseudoboehmite is performed by a one-pot method, unlike the conventional method of performing the reaction first in a basic solution, and then performing redispersion in an acidic solution, thereby simplifying the production process, and thus, may be useful in the production industry of a separator for a secondary battery, and the like.