Cassava starch is degraded by UV irradiation, particularly when previously acidified with lactic acid. Gamma irradiation also induces starch degradation through the formation of free radicals. The aim of this work was to confirm the hypothesis that free radicals are formed in starch through UV treatment and to compare free radical formation and the extent of degradation in native or acidified starches as a result of UV and gamma irradiation. Both types of irradiation result in a decrease in starch intrinsic viscosity. Electronic spin resonance (ESR) shows that radicals formed in UV irradiated samples are similar to those produced by gamma irradiation.