Disclosed is a composite for forming a coacervate interfacial film. The composite for forming the coacervate interfacial film contains a cationic hectorite nanoplate-shaped particle structure containing a hectorite nanoplate-shaped particle and a cationic surfactant coupled to a surface of the hectorite nanoplate-shaped particle, and an anionic cellulose nanofibril containing an anionic functional group in at least a portion thereof, in which the composite may form the coacervate interfacial film at an interface of an oil phase and a water phase through electrostatic interaction between the cationic surfactant and the anionic functional group.