The impacts of protein oxidation on the droplet size and microrheology properties of casein emulsions with 20% oil content were investigated. The degree of protein oxidation was indicated by carbonyl concentration. The droplets in the emulsions of different-oxidation-degree casein had bimodal distribution, but their size altered due to oxidation. The effects of protein oxidation on the morphology, motion type, viscoelasticity, and stability of droplets were also investigated by microrheology analysis. The droplet motion was blocked by protein oxidation due to mean square displacement slope results. Solid–liquid balance values provided the liquid behavior dominating these emulsions. Oxidation of carbonyl concentration 16.72 raised the primary droplets, increased the elasticity, decreased the viscosity, and promoted the droplet motion rate, resulting in better stability of emulsions. Further oxidation promoted the aggregation of droplets and resulted in poor stability.