Two new sesquiterpenoids—13-hydroxycurzerenone (1) and 1-oxocurzerenone (2)—have been isolated from the rhizomes of Curcuma zedoaria, together with 13 known compounds (3–15). The structures of two new compounds were determined through spectroscopic and MS analyses. Among the isolated compounds, 13-hydroxycurzerenone (1), 1-oxocurzerenone (2), curzerenone (3), germacrone (4), curcolone (5), procurcumenol (6), ermanin (7), curcumin (8), and a mixture of stigmast-4-en-3,6-dione (12) and stigmasta-4,22-dien-3,6-dione (13) exhibited inhibition (with inhibition % in the range of 21.28%–67.58%) against collagen-induced platelet aggregation at 100 μM. Compounds 1, 5, 7, 8, and the mixture of 12 and 13 inhibited arachidonic acid (AA)-induced platelet aggregation at 100 μM with inhibition % in the range of 23.44%–95.36%.