PROBLEM TO BE SOLVED: To provide a magnetic sheet composition, a magnetic sheet using the magnetic sheet composition, capable of reducing unnecessary electromagnetic waves emitted from electronic equipment and of suppressing electromagnetic troubles produced on the electronic equipment, which has low temperature-quick hardening properties and which restricts release of halogen ion to prevent wiring corrosion, even when it is used around wiring, and further, does not adversely affect the environment. SOLUTION: The magnetic sheet composition includes at least a binder, magnetic core, and a hardener, and the binder contains thermosetting organic resin, and the hardener contains sulfoniumborate complex, represented by formula (1), wherein R 1 is an aralkyl group, R 2 is a lower alkyl group, and X is a halogen atom, with n being 0 to 3 integer. COPYRIGHT: (C)2010,JPO&INPIT