Understanding the role of sequence and structure in the action of molecular chaperone proteins is vital for the development of peptide-based drugs with enhanced chaperone activity for the treatment of protein deposition diseases such as Alzheimer’s disease, Parkinson’s disease, type II diabetes and systemic amyloidosis. Milk casein proteins from several species have been shown to act as chaperones whereby they stabilise proteins under stress conditions to prevent their aggregation. β-Casein is one of the major caseins in milk that is naturally cleaved at one of three positions by plasmin to yield three C-terminal fragments (γ₁, γ₂ and γ₃). In an effort to determine the sequence properties most important for β-casein chaperone activity, we investigated the ability of the γ-caseins to act on the two major pathways by which proteins aggregate, i.e. via the formation of disordered, amorphous aggregates or ordered amyloid fibrils. Here we show that β-casein functions more effectively as a molecular chaperone than its fragments, leading to a reduction in both disordered and ordered aggregation of a variety of target proteins. The amphiphilic nature of β-casein likely facilitates its chaperone ability; the hydrophobic C-terminus binds to and stabilises partially unfolded target proteins while the hydrophilic N-terminus maintains the solubility of the resulting complex. The reduced chaperone ability of γ-casein may be attributable to a loss of solubility and amphiphilicity upon loss of the N-terminal fragment of β-casein. This study highlights the importance of amphiphilicity for the functioning of holdase-type molecular chaperones.