The present invention provides a sealing component for connector waterproofing having an excellent heat resistance, low-temperature resistance and oil resistance which can be economically produced in a reduced molding time. A novel sealing component for connector waterproofing is provided, which comprises a vulcanized composition comprising at least (a) 100 parts by weight of an organopolysiloxane represented by the following average composition formula (I), (b) from 5 to 500 parts by weight of a finely divided silica filler, (c) from 0.01 to 5 parts by weight of a dialkyl peroxide or peroxy ketal which has a half-life of 1 hour at a temperature of from 130.degree. C. to 150.degree. C., (d) from 0.1 to 5 parts by weight of a silicon compound having two or more Si--H bonds per molecule, and (e) from 0.01 to 2 parts by weight of an organic peroxide represented by the following general formula (II):R.sup.1.sub.m SiO.sub.(4-m)/2 (I)wherein R.sup.1 represents a substituted or unsubstituted monovalent hydrocarbon group; and m represents a positive number of from 1.98 to 2.02; ##STR1## wherein X represents a C.sub.2-8 unsubstituted divalent hydrocarbon group; and R.sup.2 and R.sup.3 may be the same or different and each represent a C.sub.3-10 monovalent hydrocarbon group or a group represented by --SiR.sup.4.sub.3 (in which R.sup.4 represents a methyl, ethyl or phenyl group).