Abstract: The mass spectra of the ketonic, alkanic and alcoholic types of bis(4′-benzo-15-crown-5)s (1a-d, 2a-d and 3a-d, repectively) under 70 eV electron bombardment were investigated. It was found that the fragmentation starting whether on the polyether rings or on the bridged chain is dependent upon the types of the bridgehead structures, α- or β-fragmentation was initially occurredon the bridged chain of the ketonic bis(crown ether)s (la-d) and then cleavage of the polyether rings followed. But the alkanic his(crown ether)s (2a-d) fragmented reversely. The alcoholic bis (crown ether)s (3a-d) dehydrated at first on the bridged chain to form (M—18)~+ or (M—36)~+ ions. The former then cleaved on the bridged chain into two large fragment ions which cleaved successively on the polyether rings into smaller ones. The bridged chains of the (M—36)~+ions seem more stable, so that the further fragmentation toke place on the polyether rings. In addition to that all the three types of bis(crown ether)s lossed m/z 45, 89 and 133 from the fragmentation of the polyether rings as the common ions, there were some characteristic fragment ions belonging to different types of the his(crown ether)s such as m/z 163 and 178 for 1a-d, m/z 149 and (M—n×44) for 2a-d, and m/z 165 and 175 for 3a-d.