Ten dimeric and two monomeric Erythrina alkaloids, all of them are undescribed, were isolated from the bark of Erythrina variegata L. and named as erythrivarines O-Z. Their structures were determined on the basis of NMR and UV-spectroscopy and mass spectrometry. Dimeric Erythrina alkaloids with a C-10/11' linkage in erythrivarine O and a C-7/10' connectivity in erythrivarines P-U are not yet reported. The two identified monomeric alkaloids may be the precursors of the described dimeric derivatives. These co-occurring dimeric and monomeric alkaloids enabled us to propose a possible biosynthetic pathway leading to these dimers. Their effects of preventing hearing loss were additionally evaluated and erythrivarine T showed as a potential protector of the House Ear Institute-Organ of Corti 1 (HEI-OC-1) cells against neomycin.