In the amyloid plaques of Alzheimer's disease (AD) patients, a large number of N-terminal-truncated amyloid beta (A beta) peptides such as A beta(11-40) have been identified in addition to the full-length A beta peptides. However, little is known about the roles of the N-terminal-truncated peptides in AD pathological process. Herein, seeding and cross-seeding aggregations of A beta(40) and its N-terminal--truncated A beta(11-40) were investigated in the solution and on the surfaces of chips with immobilized seeds by extensive biophysical and biological analyses. The results showed that A beta(40) and AA beta(11-40) aggregates could seed both homologous and heterologous aggregations of the two monomers. However, the capability and characteristics of the seeding (homologous aggregation) and cross-seeding (heterologous aggregation) were significantly different. A beta(40) seeds showed stronger acceleration effects on the aggregations than A beta(11-40) seeds and induced beta-sheet-rich fibrous aggregates of similar cytotoxicities for the two monomers. This indicates that A beta(40) and A beta(11-40) had similar aggregation pathways in the seeding and cross-seeding on A beta(40) seeds. By contrast, A beta(11-40) seeds led to different aggregation pathways of A beta(40) and A beta(11-40). Pure A beta(11-40) aggregates had higher toxicity than A beta(40) aggregates, and as seeds, A beta(11-40) seeds induced A beta(40) to form aggregates of higher cytotoxicity. However, homologous A beta(11-40) aggregates induced by A beta(11-40) seeds showed lower cytotoxicity than pure A beta(11-40) aggregates. The results suggest that A beta(11-40) plays an important role in the pathological process of AD.