Hydrodistilled volatile oils from the aerial parts of Ducrosia anethifolia and Ducrosia flabellifolia were investigated by gas chromatography (GC) and GC/mass spectrometry (GC/MS). The plants were collected from west and southwest Iran. Thirty-two compounds in D. anethifolia and thirty-three compounds in D. flabellifolia were identified, representing 93.4% and 88.2% of the total oils, respectively. The major components of D. anethifolia oil were dodecanal (28.8%), decanal (21.1%), (2E)-tridecen-1-al (15.8%) and (2E)-dodecenal (13.4%). The most abundant components in essential oil of D. flabellifolia were decanal (32.8%), dodecanal (32.6%), decanol (4.3%) and (2E)-tridecen-1-al (3.3%). Cytotoxic activity assessed on three human cancer cell lines (K562, LS180 and MCF-7) showed that essential oil from D. anethifolia represented good to moderate cytotoxic activity, while D. flabellifolia had a moderate to weak activity.