Two new monoterpenes, 3-(2-oxo-4-methyl-3-pentenyl)furan-5H-2-one (1) and 3-[(2E)-4-hydroxyl-4-methyl-2-pentenyl)]furan-5H-2-one (2), along with eight known compounds (3-10), were isolated from the stalks and infructescence of Sibiraea laevigata. Their structures were elucidated by spectroscopic methods including extensive 1D and 2D NMR techniques. In addition, all of these isolates were evaluated for their cytotoxic and antioxidant activities. The results showed that compounds 5-7 displayed cytotoxicity with IC50 values ranging from 34.8 to 43.2 μg ml-1 against tumor cell lines. Furthermore, 5 and 9 showed antioxidant activities.