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.