Abstract: Fifteen alkaloid compounds were isolated from the 70% aqueous alcohol extract of Stephania tetrandra S. Moore by silica gel, reversed phase silica gel, Sephadex LH-20 column chromatography and semi-preparative high performance liquid chromatography. They were identified as tetrandraside A (1), (Z)-N-formyl-nornuciferin (2), (E)-N-formyl-nornuciferin (3), salutaridine (4), salutaridine N-oxide (5), (E)-3-(4-hydroxy-3-methoxyphenyl)-N-2-(4-hydroxy-3-methoxyphenyl)ethyl-2 propenamide (6), dauriporphine (7), sinomenine (8), liriodenine (9), α-magnoflorine (10), (1S)-4'-β-glucosylcoclaurine (11), tetrandrine (12), fangchinoline (13), tetrandrine 2'-β-oxide (14), and tetrandrine 2'-α-oxide (15), respectively, by MS, NMR and single crystal diffraction. Among them, compound 1 is a new alkaloid glycoside. Compounds 2-11 were obtained from this plant for the first time. These compounds showed obvious cytotoxic activity against drug-resistant lung cancer cell line H1299, and compound 9 had the best activity, with an IC₅₀ of 5.38 μmol·L^-1.