Organic silicon compounds of formula (1) are novel. ##STR1## In the formula, wherein R.sup.1 and R.sup.2 are monovalent C.sub.1-8 hydrocarbon group, R.sup.3 is a C.sub.2-6 alkylene group or a C.sub.2-6 alkylene group containing at least one --C--O--C-- linkage, R.sup.4 is a C.sub.1-6 alkyl group, Rf is a C.sub.1-15 perfluoroalkyl or perfluorocycloalkyl group or a C.sub.1-20 perfluoroalkyl or perfluorocycloalkyl group containing at least one --C--O--C-- linkage, and n=0, 1 or 2, m=1 or 2, and k=2, 3 or 4. The organic silicon compounds are useful source materials for the manufacture of fluorinated polysiloxanes having solvent resistance, chemical resistance and release property.