The localization of polyisoprene in the young stem tissues of Eucommia ulmoides was investigated by histochemical staining and Fourier transform infrared microspectroscopy (FT-IR). The fibrous structures were stained using Oil Red O. FT-IR microspectroscopy analysis proved that the fibrous structures were indeed trans-polyisoprene. The presence of granular structures clearly stained by the dye and having a characteristic absorption at 2960 cm-1 in the FT-IR analysis suggested that trans-polyisoprene accumulated in the vicinity of the cambium layer. We have successfully demonstrated the localization of trans-polyisoprene in plant tissues for the first time, and our histological investigation has allowed us to deduce the main sites of biosynthesis and rubber accumulation.