The present invention relates to 1,3-dioxoisoindole derivatives of Formula (1) or pharmaceutically acceptable salts thereof, a preparation method thereof and use thereof as a T-type calcium channel antagonist, based on the fact that 1,3-dioxoisoindole derivatives of Formula (1) show selective antagonistic activity against T-type calcium channel, thus being effective in treating brain diseases, cardiac diseases and neurogenic pains: ##STR00001## wherein R.sub.1 is a phenyl or a benzyl group, optionally substituted with a moiety selected from the group consisting of a halogen atom, a C.sub.1-C.sub.6 alkoxy, a C.sub.1-C.sub.6 alkyl, and a cyano group; R.sub.2 is a heterocyclic group selected from the group consisting of piperidinyl, pyrrolidinyl, morpholinyl, and piperazinyl groups, wherein the heterocyclic group is optionally substituted with a C.sub.1-C.sub.6 alkyl group; and n is 1 or 2.