It was found that the product of cometathesis of allyltrisubstituted silanes and 1-decene in the presence of different complexes of ruthenium was (E)-and (Z)-R3SiCH=CHR1 (R = Me or EtO; R1 = n-C8H17.). The cometathesis was accompanied by the migration of a double bond in allylsilanes and 1-decene. The isomerization of allyltrisubstituted silanes to appropriate propenyltrisubstituted silanes as well as of 1-, 2-, and 4 - alkenes to isomeric alkenes in the presence of ruthenium complexes was investigated too. It was proved that the migration of a double bond is accompanied by (E) - (Z) isomerization. Products of the first stage of the migration reaction are mainly (E) isomers. Isomerization proceeds at lower temperatures than cometathesis. Tetrachloroethylene as a solvent was favorable for isomerization, but it inhibited cometathesis.