A new lupin alkaloid, (-)-Δ5-dehydroalbine, was isolated from the ethanol extract of the seeds of Lupinus termis together with some unusual lupin alkaloids, (-)-albine, (-)-11,12-seco-12,13-didehydromultiflorine and (-)-13α-hydroxymultiflorine. The structure of the new alkaloid (1) was presumed to be (-)-Δ5-dehydroalbine on the basis of its spectroscopic data. The unusual type of lupin alkaloids substituted at C-13 such as (-)-albine and (-)-Δ5-dehydroalbine are assumed to be derived possibly from (-)-13α-hydroxymultiflorine via an aza-Cope rearrangement as the key step. © 1991.