? 2014, Japan Journal of Food Engineering. All rights reserved. β-Carotene was encapsulated by self-aggregated caseinates, and the encapsulation efficiencies and storage stabilities of the resultant spray-dried powder were investigated. The pH of the sodium caseinate solution, which determined the degree of aggregation, tremendously af fected the encapsulation yield and storage stability of β-carotene in the spray-dried powder. We found that at pH 6.0, the resultant powder showed excellent encapsulation property compared to other pH conditions (pH＝6.5, 5.5). Small angle X-ray scattering analysis revealed that the representative sizes of the aggregates in the sodium caseinate solution at pH 6.5, 6.0, and 5.5 were approximately 91, 111, and 166 nm, respectively. This analysis also clarified that our system represented fractal growth aggregation while the surface fractal dimension increased with decreasing pH. Apparently, the encapsulation property was affected by the physical properties of the aggregates, and there existed an optimal aggregation degree, which maximized the performance of an encapsulated system.