Starch is isolated from the Andean tubers olluco (Ollucus tuberosus) and oca (Oxalis tuberosa) and modified with octenylsuccinic anhydride (OSA); subsequently, the morphological, molecular, and physicochemical characteristics are evaluated. The isolated starch of olluco and oca results in a powder with a purity of 93.2 and 92.8%, respectively; the amylose content of starch isolated from olluco and oca are 27.1 and 28.2%, respectively. The degree of substitution of OSA starch are 0.015 and 0.016 for olluco and oca, respectively. The peak viscosities of OSA starches ranges from 2.83 to 2.88 Pa · s and are higher than those of native starches. The gelatinization temperature and enthalpy of native starches are higher than those of OSA starches. A B-type X-ray diffraction pattern is observed for native and OSA starches, and the crystallinity of OSA starches is less than that of its native counterparts. Fourier transform infrared spectroscopy (FTIR) shows a decrease in the 995/1022 cm−1 ratio in OSA starches but not in native starches, which indicates an alteration of the double helical structure; FTIR shows two new peaks after modification with OSA (1724 and 1572 cm−1). Andean tubers can be used an alternative source for producing chemically modified starch with practical applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim