A chemical investigation of Cynanchum mongolicum (Maxim.) Kom. identified 8 compounds. On the basis of spectroscopic data, they were determined to be 3 alkaloids and 5 sinapoyl esters, among which were two previously undescribed compounds (1 and 2). The inhibitory effects of the isolated compounds against four human tumor cell lines were evaluated in vitro by MTT assays, which revealed moderate inhibitory effects with IC50 values < 50 mM, in particularly, three antofine analogues have showed significant antitumor activities with IC50 values < 0.1 mM, which was obviously better than the 5-fluorouracil and potential to be used as cancer drugs. © 2019 Informa UK Limited, trading as Taylor & Francis Group.