The reaction betweon bromine and 8-methogypsoralen(1) and that between NBS and 1 have been studied in detail. It was shown that at first the hydrogen at 5 position of 1 was substituted by bromine, then a molecule of bromine was added onto 4', 5' double bond and finally another moleoule of bromine was added onto 3, 4 double bond. It was clearly demonstrated that 3, 4 double bond of 1 is reactive toward bromine or NBS. This reaction has not been reported previously and the new compound, 3, 4, 5, 4', 5'-pentabromo-3, 4, 4', 5'-tetrahydro-8-methoxypsoralen (4),was obtained.