Polybutadiene (I) containing 91% 1,4-(cis/trans) units and 9% of 1,2 units, in the presence of vinyltriethoxysilane and ruthenium catalysts Cl-2(PCy3)(2)Ru = CHPh (II) and [RuCl2(p-cymene)](2)/N2CHSiMe3/PCy3 (III) at 60 degrees C and at room temperature undergoes partial degradation and functionalization. At a ratio [vinylsilane]/[total >C=C < of (I)]=0.1, the reaction leads to a limited (compared to ethylene as a substrate) degradation and metathetical conversion of 1,4-polybutadiene (particularly cis-CH=CH units) with vinylsilane yielding silylated unsaturated oligomers. At a ratio [vinylsilane]/[total > C=C < of(I)]=1, a cross-metathesis of 1,2 >C=C < groups of (I) with vinylsilane predominated over the degradation/cross-metathesis of 1,4-polybutadiene.