Rhizoma Smilacis Glabrae (RSG) and Rhizoma Smilacis Chinae (RSC) are two herbal materials that belong to the same genera and are both listed in the Chinese Pharmacopoeia. Chemical constituents in the two species were compared by HPLC-DAD-MS/MS. Many common constituents were found in both species, including shikimic acid, 5-O-caffeoylshikimic acid, trans-resveratrol, taxifolin, astilbin and its three stereoisomers, engeletin and isoengeletin. However, syringic acid was found only in RSG, while chlorogenic acid was found only in RSC.