The catalytic activity of heterogeneous catalytic systems based on molybdenum halides immobilized onto the silica gel surface in combination with organosilicon cocatalysts has been studied in a model reaction of hexene-1 metathesis at 27 and 50A degrees C. It has been established that quite active catalysts are formed when using 1,1,3,3-tetramethyl-1,3-disilacyclobutane or triethylsilane as cocatalysts. Tetramethylsilane has exhibited no marked activity, while tetramethyltin has turned out to be the most effective cocatalyst. Possible routes of formation of active centers have been proposed for organosilicon cocatalysts.