Artemyriantholidimers A-G (1-7), seven undescribed guaiane-type sesquiterpenoid dimers (GSDs), and 27 known compounds (8-34) were isolated from Artemisia myriantha (Asteraceae). Their structures and relative configurations were elucidated based on the comprehensive analyses of UV, IR, MS, NMR data, quantum chemical NMR calculations with DP4+ probability analyses, and the absolute configurations were elucidated by ECD calculations. The undescribed GSDs (1-7) were presumably formed via Diels-Alder reactions, and compounds 5-7 were rare GSDs with α-configuration of H-6'. Compounds 4-7 showed significant inhibition on HepG2, Huh7, and SK-Hep-1 cells with IC