A polysiloxane containing an ethylidene norbornyl group possesses a terminal group represented by the formula: ##STR1## wherein R.sup.1 stands for a monovalent hydrocarbon group, a hydroxyl group, an alkoxy group, or at least one of the hydrocarbon groups represented by Y, and each R.sup.2 stands for the same or different groups selected from the class consisting of hydrogen, monovalent hydrocarbon groups, and a group represented by R.sup.1 wherein R.sup.1 has the same meaning as defined above, and being substantially in the form of a straight chain, 0 to 100 mol %, providing that 100 mol % is excluded where neither of the R.sup.1 's in the terminal groups is a hydrocarbon group represented by Y of the component units being represented by the formula: ##STR2## wherein each R.sup.3 's stand for the same or different groups selected from the class consisting of hydrogen and monovalent hydrocarbon groups and 100 to 0 mol %, providing that 0 mol % is excluded where neither of the R.sup.1 's in the terminal groups is a hydrocarbon group represented by Y of the component units being represented by the formula: ##STR3## wherein R.sup.4 stands for a monovalent hydrocarbon group of 1 to 8 carbon atoms and Y stands for ##STR4## so as to bond a silicon atom to the neighboring silicon atom through an oxygen atom.