Three new coumarins containing a C 10 terpenoid side chain, clauslactones R-T (1-3), together with 14 known coumarins (4-17) and 11 known carbazole alkaloids (18-28), were isolated from the leaves and stems of Clausena excavata. Their structures were established by detailed spectroscopic analyses. Furthermore, the stereochemistry of 1 was confirmed by single-crystal X-ray diffraction analysis, which was the first example among coumarins with a C 10 terpenoid side chain. Additionally, compounds 22 and 27 were found to show moderate topoisomerase II inhibitory effects at 50 m mM.