One new p-quinonoid aporphine alkaloid, obtusipetadione (1), and eleven known compounds (2-12) were isolated from the acetone extract of the twigs of Dasymaschalon obtusipetalum. Their structures were elucidated by spectroscopic methods. The cytotoxic and antimalarial activities of the isolated compounds were evaluated. Compound 1 showed significant in vitro antiplasmodial activity against the P. falciparum strains TM4 and K1 (multidrug resistant strain) with IC50 values of 2.46±0.12 and 1.38±0.99 μg/mL, respectively with no cytotoxicity. Compound 9 had more modest antiplasmodial activity, but significant cytotoxicity.