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This work investigated the impact of power ultrasound (PUS) pretreatment on the physical and functional properties of reconstituted milk protein concentrate (MPC) 80. Ultrafiltered/diafiltered (UF/DF) milk protein retentates were treated with PUS (12.50 ± 0.31 W and 50% amplitude) for 0.5, 1, 2, and 5 min prior to spray drying. Results revealed that the particle size (D50) reduced from 28.45 μm to 0.13 μm after 0.5 min of sonication. Solubility increased significantly from 35.78% to 88.30% after 5 min of PUS pre-treatment. Moreover, the emulsifying activity index (EAI) of MPC samples increased significantly as the time of ultrasonic treatment was prolonged. Additionally, the emulsion stability index (ESI) initially increased after ultrasound treatment for 1 min. Surface hydrophobicity was greatly increased with more hydrophobic groups exposed to the environment. PUS pre-treatment also promoted an increase in the storage modulus ( G ′) of the MPC solutions. Viscosity significantly decreased after PUS pre-treatment. This result was confirmed by the microstructure of the powder, with small particles formed and trapped in dents of large particles. However, sodium-dodecyl sulfate–polyacrylamide gel electrophoresis showed no significant change in protein molecular weight.