This work studies the physicochemical, molecular, and emulsification properties of Oxalis tuberosa (oca) starch modified with octenyl succinic anhydride (OSA). Freshly harvested oca tubers are washed and selected, and starch is extracted by tuber size reductions and successive washes. Modifications are performed with OSA for 6 h at pH 8.5–9. Mean particle size increases, while temperature and enthalpy of gelatinization decrease with OSA modification. In addition, peak, breakdown, and final viscosities increase as caused by partial disorganization of starch components during chemical modifications, an effect that is exhibited by variations of X-ray diffraction type and crystallinity. Oca-OSA starch produces pastes with pseudoplastic behavior and emulsions with higher emulsification properties in comparison with the native starch. These results indicate that esterification of oca starch with OSA can be used to produce starches with desired physicochemical and emulsification properties.