Three new carbazole alkaloids, mafaicheenamine A-C (1-3), along with five know compounds (4-8) were isolated from the twitzs of Clausena lansium. All compounds were characterized by the analysis of spectroscopic methods. In addition, the evaluation of antitumoral activity against three human cancer cell lines, KB, MCF-7 and NCI-H187, of compounds 1, 2 and 4-8 were also reported.