The mass spectra of 1, 3-bridged 1, 2, 3, 4-tetrahydronaphthalenes (I, I', II, III and IV), 2, 4-bridged 1, 2, 3, 4-tetrahydroisoquinolines (VI, VII and VII') and 1, 3-bridged 1, 2, 3, 4-tetrahydroquinolines (VIII and IX) were examined. Fragmentation pathways of these compounds are discussed. The compounds I-V undergo two major fragmentations ; fission of the B-ring to give fragment ions of C-ring and A-ring, and formation of naphthalene and small nitrogen-containing fragment ions. While, the compounds VI-IX decompose to form quinoline- or isoquinoline-type fragment ions by loss of C-ring moiety. The position of nitrogen atom plays a dominant role in determining the predominance of the fragmentation.