Whey proteins and their hydrolysates are valued as important emulsifiers in foods. The purpose of this study was to produce oil-in-water nanoemulsions using whey protein isolate (WPI) hydrolysate as the emulsifier. Factors including the oil phase concentration (4 and 10% [w/w]), enzyme type (chymotrypsin and pepsin), hydrolysate emulsifier concentration (1–4% [w/w]), storage temperature (4 and 25 °C), and storage time (0–7 days) were investigated to determine their effects on the nanoemulsifying ability of WPI hydrolysate. Chymotrypsin–WPI hydrolysate formed nanoemulsion (d = 287.9–192.5 nm) whose diameter decreased as the hydrolysate concentration in the aqueous phase was increased from 1 to 4%, whereas pepsin WPI hydrolysate did not form nanoemulsions (d = > 3900 nm) due to lack of electrostatic repulsive forces between the peptide that makeup the pepsin WPI hydrolysate. However, the droplet sizes of the chymotrypsin nanoemulsions were larger than those formed by unhydrolysed WPI (d = 160.7 nm) and Tween 20 (d = 176.7 nm) but were still within the nanometre range. Additionally, the WPI hydrolysate was a better emulsifier in nanoemulsions at low oil concentration (4%) than at high oil concentration (10%), and better storage properties (minimal changes in droplet size and creaming stability) were exhibited at 4 °C than at 25 °C. This study demonstrated that WPI hydrolysates can be employed as emulsifiers in nanoemulsions that are tailored for food applications.