Volatile oils hold tremendous potential for the production of high quality plant based medicines. The aim of this study was to evaluate the cytotoxic activity of cumin volatile oil (CVO) against hepatocellular carcinoma (Hep-G₂). In MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, CVO showed potent cytotoxic activity against Hep-G₂ cell line with IC₅₀=2.4 µg/ml. Bioguided fractionation of  CVO using silica  gel column chromatography afforded two active fractions(VO-1and VO-2)  with IC₅₀= 0.6 and 0.9 µg/ml, respectively. GC-MS analysis was carried out for CVO and its two active fractions.  Crystallization of active fraction VO-1 lead to the isolation of cuminic acid with IC₅₀=6 µg/ml. The structure of cuminic acid was established using IR, MS, ¹H-NMR and ¹³C-NMR