Two new phthalide derivatives, angesinenolides A and B (1and 2), were isolated from the roots of Angelica sinensis. Their structures were elucidated using HRMS, NMR, and X-ray crystallographic data. Compound 1is the first example of a phthalide trimer presumably formed through two [2+2] cycloaddition reactions. Compound 2is a unique dimeric phthalide with a peroxy bridge between C-3a and C-6. Both phthalides were evaluated for in vitro anticoagulation activities. Compound 1reduced the level of fibrinogen (FIB). Compound 2significantly extended thrombin time and activated partial thromboplastin time, as well as markedly reduced the content of FIB.