Octenyl succinic anhydride modified starches (OSA-starches) are widely used as emulsifiers and stabilizers in the food industry. Selection of optimal OSA-starches for a given application would be facilitated with better understanding of the relations between performance and molecular structure, and the mechanistic reasons for observed correlations. Structural parameters, including molecular size distribution, chain-length distribution, degree of branching, degree of substitution (DS) and amount of small molecules such as maltose, were characterized using size-exclusion chromatography (SEC, also termed GPC) and 1H nuclear magnetic resonance (NMR), and were correlated with the functional properties of viscosity, emulsion droplet size and emulsion stability. The observed correlations varied with the methods used to make the OSA-starch, which affects gross structural features. The viscosity of OSAstarch solutions was related to starch molecular size and the relative amounts of small molecules; the DS showed positive correlation with viscosity. Emulsion droplet size is mainly determined by the whole molecular size of the OSA-starch. Emulsion stabilization efficacy is mainly affected by the average chain length. These correlations can be rationalized by basic precepts of the behaviour of polymer chains in solution and the fundamentals of electrosteric stabilization.