We have proven that xanthones 1-8 isolated from the root of C. tricuspidata possess highly potent αα-glucosidase inhibition properties. Compound 1 was identified as a new isoprenylated tetrahydroxy xanthone, 1,3,6,7-tetrahydroxy-2-(3-methylbut-2-enyl)-8-(2-methylbut-3-en-2-yl)-9H-xanthen-9-one (1). These are the first natural xanthones documented to exhibit such inhibition. The IC50 values of compounds 1-8 inhibiting α-glucosidase activity were determined to be up to 16.2 μM. Mechanistic analysis showed the xanthones 1-8 exhibited full mixed inhibition.