A new glucosidic lupin-alkaloid, (—)-(trans-4'-fl-D-glucopyranosyloxycinnamoy1)- (5), was newly isolated from the fresh seedlings of Lupinus luteus. Its structure has been confirmed by direct comparison with a synthetic material. The concentration of 5 in the immature and mature seeds of L. luteus was negligibly low, but its concentration increased rapidly during the first 3-10 day's growth of seedlings and became a minor component again in the later stages of the plant's growth. © 1979, The Pharmaceutical Society of Japan. All rights reserved.