Organic silicon compounds of formula (1) are novel: ##STR1## In the formula, R.sup.1, R.sup.2 and R.sup.3 are monovalent C.sub.1-8 hydrocarbon group, R.sup.4 is a C.sub.1-6 alkyl group, R.sup.5 is a C.sub.2-6 alkylene group or a C.sub.2-6 alkylene group containing at least one --C--O--C-- linkage, Rf is a C.sub.1-12 perfluoroalkylene or perfluorocyclo-alkylene group or a C.sub.1-12 perfluoroalkylene or perfluorocycloalkylene group containing at least one --C--O--C-- linkage, and n is 1, 2 or 3. The organic silicon compounds are useful source materials for the manufacture of fluorinated polysiloxanes having solvent resistance, chemical resistance and release property.