Abstract: One undescribed and two known furocoumarins were isolated from the stems of the Clausena lansium through a series of isolation and purification approaches including HPD-100 macroporous resin column, silica gel, reverse phase C₁₈ and so on. Their structures were determined to be 8-(2S,3S,6E)-2,3-epoxy-3,7-dimethyl-oct-6-enyloxy psoralen (1), 8-(7',8'-epoxygeranyloxy) psoralen (2) and 8-(2E)-6-oxo-3,7-dimethyloct-2-enyloxy psoralen (3) by spectroscopic methods. Compound 1 is a new furocoumarin. Compound 2 showed cytotoxicity to H460 (IC₅₀=43.94 μmol·L^-1) and compound 3 showed cytotoxicity to HeLa (33.76 μmol·L^-1) through the cytotoxic tests against five human cancer cell lines (H460, H7402, HCT-8, HeLa and MCF-7) for all compounds.