The essential oil of roots of Jatropha ribifolia, obtained by hydrodistillation, was characterized in terms of its chemical composition by chromatographic method with flame ionization detection (GC-FID) and gas chromatography coupled to electron ionization mass spectrometry (GC-MS). The analyses and identification pointed by mass fragmentation pattern and retention index revealed the presence of 49 compounds, representing 91.4% of the total oil, with 39.5% of monoterpenes, 43.0% of sesquiterpenes and 8.5% of phenylpropanoids. The major compounds of the oil were β-pinene (9.2%), isoeugenol methyl ether (8.5%), vatirenene (8.4%), α-gurjunene (7.0%), endo-8-hydroxy-cycloisolongifolene (6.6%), α-pinene (6.4%) and p-menth-1-en-8-ol (5.2%). The fractionation by preparative thin layer chromatography (TLC) allowed obtaining five fractions (F1-F5) with different compound contents from the original oil. Some essential oil components showed a significant increase in their levels after fractionation, as borneol (17.9%, F1), 3-thujopsanone (19.1%, F4), isoeugenol methylether (21.2%, F2), 8-oxo-9H-cycloisolongifolene (21.4%, F4), 8-cis-5(1H)-azulenone,2,4,6,7,8,8a-hexahydro-3,8-dimethyl-4-(1-methylethylidene) (23.1%, F4) e endo-8-hydroxy-cycloisolongifolene (38.6%, F2). These fractions and oil were tested in vitro against nine human cancer cell lines by sulforhodamine B assay. The Jatropha oil was more effective in inhibiting the growth of cells NCI-H460 (drug resistant ovarian; GI50 6.2 μg mL-1) and OVCAR-3 (ovarian; GI50 8.0 μg mL-1). The cancer cells line PC-3 (prostate) was more sensitive to the effects of the fractions showing significant values of GI50 such as for fraction F1, F2 and F4 (< 0.25 μg mL-1). In general the antiproliferative activity of the fractions was more pronounced than that of crude oil.