1-Acetyl-4-methoxy-β-carboline (I), canthin-6-one (Villa), 1-methoxycanthin-6-one (VIIIb), and canthin-6-one-3N-oxide (IXa), and three new alkaloids, 1-(2′-hydroxyethyl)-4-methoxy-β-carboline (IIa), 1-(1′,2′-dihydroxyethyl)-4-methoxy-β-carboline (IIIa), and 1-methoxycanthin-6-one-3N-oxide (IXb), were isolated from the root bark of Ailanthus altissima Swingle (Simaroubaceae). The structures of IIa, IIIa, and IXb were elucidated by spectroscopic and chemical studies. © 1981, The Pharmaceutical Society of Japan. All rights reserved.