Diallyl Phthalate compounds having a molecular weight of 250 to 20,000 and having at least one silyl group represented by the formula: ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are each a hydrogen or a monovalent hydrocarbon radicals having 1 to 10 carbon atoms, such as alkyl, aryl or aralkyl radicals; X is a group selected from halogen, alkoxy, acryloxy, aminoxy, phenoxy, thioalkoxy and amino groups, and "a" is an integer 0, 1 or 2, in the molecule; and process for producing same wherein a diallyl phthalate monomer or prepolymer having molecular weight of 20,000 or less is reacted with a hydrosilane compound having the formula: ##STR2## wherein the designations are the same as above, and at a temperature within the range of 50.degree. to 150.degree. C.