A possible role of rubber in the Hevea brasiliensis tree was presumed based on the analysis of structural changes of rubber during storage in the rubber tree as latex. The rubber obtained from a previously untapped mature-tree, a so-called virgin mature-tree (Vir-NR), contained a gel fracation higher than 80;. The gel fraction showed almost the same structure as a corsslinked rubber prepared from fresh latex in the presence of peroxide, with the molecular weight of a primary segment between crosslinks (Mc) of 3 x 103. The sol fraction from Vir-NR was an oxidative degraded product containing aldehyde and epoxide groups. The gel fraction from a regularly tapped mature-tree (Reg-NR) was less than 3;and was loosely crosslinked with hydrogen bondings and ester linkages, having Mc of 7 x 10 5. These indicate that rubber accepts radicals, to form C-C crosslinking and partly oxidative degradation products in laticiferous tubes of Hevea tree during storage, suggesting a possible role of rubber as a scavenger of hydroxy radicals in latex.