Three novel carbazole alkaloids, named clausamine-A (1), -B (2), and -C (3) were isolated from Clausena anisata (Rutaceae) collected in Thailand, and their structures were elucidated by means of spectroscopic analyses. All these novel carbazoles have 1-oxygenated 3,4-disubstituted structures with a lactone moiety. This is the first report of the isolation of lactonic carbazole alkaloids from a natural source.