A compound containing two fluorosulfonyl groups which are groups convertible to sulfonic acid groups, an intermediate therefor, and methods for their production with high productivity, are provided. Also provided are a fluorosulfonyl group-containing polymer obtained by polymerizing such a compound, and a sulfonic acid group-containing polymer obtained from such a polymer.A method for producing a compound of the following formula (m0), such a compound, a fluorosulfonyl group-containing polymer obtained by polymerizing such a compound, and a sulfonic acid group-containing polymer obtained from such a polymer, provided that R.sup.F01 is a single bond or a C.sub.1-6 bivalent perfluoro organic group, R.sup.F02 is a C.sub.1-6 bivalent perfluoro organic group, and n is 0 or 1: ##STR00001##