A new biflavonoids, (2R,2''R)-7-O-methyl-2,3,2'',3''-tetrahydrorobustaflavone (1), along with five known flavonoids (2-6) were isolated from the MeOH extract of Aster tataricus. Among them, compounds 1-2 were the C-3'-C-6'' type biflavonoids obtained from the genus Aster for the first time. The structures and absolute configurations of compound 1 was confirmed based on extensive spectroscopic and circular dichroism analyses. Compound 1 exhibited moderate cytotoxicity against seven human cancer A549, HepG2, PC3, DU145, MCF-7, LOVO and NCI-H1975 cell lines....