The chloroform soluble fraction of the methanolic extract of the aerial parts of Tanacetum santolinoides afforded six sesquiterpene lactones. Tanacetolide A (1) was isolated for the first time from a natural source, in addition to five known sesquiterpene lactones. The structures were established on the basis of extensive studies of their 1D and 2D (1H-1H COSY,HMQC, HMBC, HOHAHA and NOESY) NMR spectra and FAB mass spectral determinations. The compounds showed good
cytotoxic activity when tested using the brine shrimp bioassay.