The impact of lipid oxidation on protein modifications in emulsions and the consequences on protein digestibility remains unclear. In this study, this impact is evaluated in casein (6 mg mL−1) based emulsions containing oxidized soybean or fish oil (3%) in presence (0.3%) or absence of the emulsifier Tween 20. Emulsions are prepared using oils at three oxidation levels and subsequently the impact on protein digestibility is evaluated after 24 h incubation at 4 °C. Remarkably, protein digestibility increass in emulsions containing medium and highly oxidized fish oil: 70 ± 0.4% and 73 ± 0.4% of the proteins are digested, respectively, whereas protein digestibility in emulsions containing low oxidized fish oil amounted to 63 ± 0.4%. Protein digestibility in emulsions containing soybean oil stabilized by Tween 20 is not influenced by the oxidation level of the oil used. A remarkable tendency is observed for the malondialdehyde content of the emulsions depending on the presence of Tween 20. For soybean oil based emulsions, malondialdehyde concentrations are consistently higher in the presence of Tween 20. On the other hand, for the fish oil based emulsions an opposite trend is observed, except at the highest oxidation level evaluated, for which no significant differences can be detected. It is concluded that the composition of the interface in emulsions depends strongly upon the degree of oil oxidation and the presence of other emulsifiers. If the oil is more oxidized, less protein is present in the interface restricting the impact of lipid oxidation products on the proteins and hence their digestibility. Practical Applications: This research was done to highlight the relevance of the interfacial composition in food emulsions and its influence on dairy protein digestibility. The food industry must be aware of the oil quality and the presence of emulsifiers in foods emulsions that allow to preserve the stability and nutritional characteristics of these food emulsions. This article aims to evaluate the impact of the reactions occurring between lipid oxidation products and proteins in emulsions on protein digestibility. This impact is evaluated in casein based emulsions containing oxidized soybean or fish oil (3%) in presence or absence of an emulsifier (0.3%). Emulsions are prepared using three oxidation levels and subsequently the impact on protein digestibility is evaluated after 24 h incubation at 4 °C. It is concluded that the composition of the interface in emulsions depends strongly upon the degree of oil oxidation and the presence of other emulsifiers.