In the continuing discovery and structure elucidation of natural xanthone dimers, which are still rarely reported in absolute confguration, three new xanthone dimers, eumitrins I–K (1–3) were isolated from the lichen Usnea baileyi, a rich source of natural xanthone dimers. Their structures were elucidated unambiguously by spectroscopic analyses, including high-resolution electrospray ionization mass spectrometry (HRESIMS), 1D and 2D nuclear magnetic resonance spectroscopy (1D and 2D NMR). The absolute confguration of all three compounds was established through DP4 probability and ECD calculation. All compounds revealed weak activity for their enzymatic inhibition against α-glucosidase and tyrosinase, as well as antibacterial activity. Keywords: Lichen · Usnea baileyi · Dimeric xanthone · α-Glucosidase · Enzyme inhibitory · Antibacterial.