The chain length and geometric isomerism of polyprenols from Eucommia ulmoides Oliver were analyzed using supercritical fluid chromatography. After intensive effort to establish separation conditions for geometric isomers, a phenyl-bonded silica gel-packed column was found that cleanly separated poly-trans and -cis prenols. The presence of long-chain poly-trans prenols (>9 mers) was confirmed for the first time in plants. Trans isomers were found in the leaf, seed coat, and root, but not in the bark and seed. Poly-trans prenols in this plant may act as intermediates for trans-polyisoprene biosynthesis.