Abstract: The chemical constituents of the aerial parts of Euphorbia antiquorum (family Euphorbiaceae) were investigated. From the EtOAc partition of the 90% EtOH extract of the title species, thirteen compounds were separated by silica gel, octadecylsilyl silica gel and Sephadex LH-20 column chromatographies, as well as semi-preparative HPLC. The structures of these isolates were characterized as five pimarane-type (1-5), two abietane-type (6, 7) and six atisane-type (8-13) diterpenoids on the basis of spectroscopic analyses (MS, NMR, ECD, etc.). Among them, compounds 1 and 6 were identified as two previously unreported ones. The α-glucosidase inhibitory activity of selective diterpenoids was further evaluated in the current work. Compound 1 exhibited moderate inhibition against the enzyme, with an IC₅₀ of 150.03 ± 3.41 μmol·L^-1, being lower than that of the reference drug acarbose.