Chaparrinone (1) and 6alpha-tigloyoxychaparrinone (2) were shown to be responsible for the antitumor and cytotoxic activities of the root bark of Ailanthus integrifolia ssp. calycina. The structure of the latter compound was established by analysis of spectral data. Compound 2 exhibited a more pronounced biological activity than chaparrinone (1) and demonstrates, for the first time, anticancer activity of a simaroubolide ester substituted at only the 6-position.