Abstract The hydrophilicity of nanocellulose materials mitigates their good mechanical and oxygen barrier properties when exposed to humid conditions. It also limits nanocellulose use in many applications where water is present. This study reveals hydrophobic modification of cellulose nanofiber (CNF) films with vinyl esters of variable alkyl chain length using deep eutectic solvent (DES) of imidazole and triethylmethylammonium chloride as a reaction medium. Additionally, the influence of ultraviolet-ozone (UV/O₃) pretreatment on CNF film modification in DES was addressed. The esterification of CNF films in DES was proven to be a simple and fast approach to increase the hydrophobicity of the films (increasing the contact angle from 38° to 107°), requiring only a 15 min reaction time and reaction temperature of 80 °C. Moreover, the modification improved water vapor barrier properties of the films and resulted in improved mechanical properties at wet state, especially with films treated with UV and ozone before modification.