One new sesquiterpenoid alkaloid, namely 3 beta, 8 alpha-dihydroxy-13-pyrrolidine-4(15), 10(14)-(1 alpha H, 5 alpha H, 6 beta H, 11 beta H)- guaiadien-12,6-olide (1), together with two known guaiane-type sesquiternoids (2 - 3) was isolated from the aerial part of Acroptilon repens. The structure of 1 was established by spectroscopic methods, especially 2D NMR (HMQC, HMBC, and NOESY). Cytotoxic activity against tumor cell line was assessed for compounds 2 - 3, and found to show potent cytotoxic activities against tumor cell line P-388.