The contents and composition of fructans in underground organs (rhizophores) of Vernonia herbacea (Veil.) Rusby, a perennial herb native to the Brazilian cerrado, were analyzed at different phenological stages. Fructopolysaccharides were always present in higher concentrations than oligosaccharides but variations in amounts of both fractions occurred together. A marked decline in total fructan and an increase in free fructose were observed between sprouting and flowering, suggesting the occurrence of hydrolysis in association with the growth of new aerial shoots and flower development. There were higher amounts of total fructan at the end of summer and at dormancy, alternating with lower amounts at early dormancy. In spite of these variations the mean molecular mass of the fructo-polysaccharides remained nearly constant throughout the cycle, except for the higher value found in vegetative plants at the end of summer. The maintenance of the mean molecular mass of fructo-polysaccharides in the flowering phase concurrent with a marked reduction in total fructans suggests a peculiar mechanism of depolymerization in this plant, while the variation pattern found for fructan contents over the phenological cycle points to their role as reserve compounds in Vernonia herbacea.