Twelve prenylated carbazole alkaloids, containing a novel prenylated carbazole alkaloid, named as clausevestine (1), and 11 known prenylated carbazole alkaloids (2-12), were isolated and identified from the stems and leaves of Clausena vestita, which is a Chinese endemic plant. The chemical structure of 1 was established by means of comprehensive spectroscopic data analyses and the known compounds were determined via comparing their NMR and MS data as well as optical rotation values with those reported in literature. Especially, clausevestine (1) is an unusual prenylated carbazole alkaloid possessing an unprecedented carbon skeleton holding 20 carbon atoms. The anti-inflammatory effects and antiproliferative activities of those isolated prenylated carbazole alkaloids were tested. Prenylated carbazole alkaloids 1-12 displayed remarkable inhibitory effects on NO (nitric oxide) production with IC values equivalent to that of the positive control (hydrocortisone). Meanwhile, prenylated carbazole alkaloids 1-12 exhibited remarkable antiproliferative activities against diverse human cancer cell lines in vitro holding the IC values ranging from 0.32 ± 0.04 to 18.76 ± 0.18 µM. These findings indicate that these prenylated carbazole alkaloids possessing remarkable anti-inflammatory effects and antiproliferative activities could be meaningful to the discovery of new anti-inflammatory and anti-tumor candidate drugs.