To provide a thermosetting resin composition that produces a cured product having high heat resistance, i.e., a high glass transition temperature by using as a curing agent for a thermosetting resin a polyamine borate produced by reacting a polyamine-based compound and an inexpensive boric acid to introduce a borate group at a molecular level into a thermosetting resin such as an epoxy resin, a novolac phenolic resin or the like.

A thermosetting resin composition comprises as the essential components a thermosetting resin and a polyamine borate as a curing agent for the thermosetting resin resulting from the reaction of a polyamine-based compound and an inorganic boric acid compound represented by formula (1): B(OR)n(OH)3-n (wherein n denotes an integer of 0-3; R denotes an alkyl group of CmH2m+1; and m denotes an integer of 1-10).