Two new piperidine alkaloids, pipernonaline and piperundecalidine, were isolated from fruits of Piper longum L. (Piperaceae). Their structures were determined to be (2E,8E)-N-[9-(3α-methylenedioxyphenyl)-2,8-nonadienoyl]piperidine and (2E,4E, 10E)-AT-[ll-(3,4-methylenedi-oxyphenyl)-2,4,10-undecatrienoyl]piperidine, respectively, on the basis of spectral data. © 1983, The Pharmaceutical Society of Japan. All rights reserved.