The stereoisomeric composition of 1,6-dienes as the main (70-80%) desired products of cyclopentene comethathesis with hexene-1 and octene-1 and symmetric olefins (decene-5 and tetradecene-7) that are the products of hexene-1 metathesis with octene-1 were studied depending on the conversion of cyclopentene at different temperatures and reaction conditions (hexene-1 : cyclopentene molar ratio, presence of triphenylphosphine additives) over the MOCl5/SiO2-SnMe4 catalyst system. It was shown that, at cyclopentene conversions of 1-55%, the amount of thermodynamically less favorable 1,Z-6-undecadiene and 1,Z-6-tridecadiene was 80-50%, whereas the amount of the metathesis products Z-decene-5 and tetradecene-7 was 25-16%. The stereoisomeric composition of 1,6-undecadiene and 1,6-tridecadiene tends to the thermodynamically equilibrium composition (Z/E = 16 : 84) with an increase in the cyclopentene conversion and reaches this composition at the equilibrium conversion of cyclopentene (77%, 25 degrees C). The chemical and stereomeric compositions of the cometathesis products are independent of the length of the alpha-olefin carbon chain.