Background: Haplophyllum tuberculatum is a plant belongs to family rutacee. It is rich in volatile oils, fixed oils, alkaloids, and furanocoumarins. It is well known for the huge number of folkloric uses in middle east. Objective: The aim of this study is to establish the chemical composition of the essential oils of Libyan H. tuberculatum and to investigate their cytotoxic potentialities. Materials and Methods: The essential oils of the aerial parts and flowers of H. tuberculatum growing in Libya were prepared by hydrodistillation. GC/MS analyses were performed on a Shimaduz capillary gas chromatograph (GC 17A ver.3) instrument directly coupled to mass spectrometer-MS QP5050A. Oil A and F of H. tuberculatum at different concentrations (0-50 µg/ml) in DMSO were tested for cytotoxicity against human tumor cell lines. Results: Oil yield was found 0.4 and 1.5 (v/w %) on dry weight basis respectively. GC/MS analysis resulted in identification of total 35 compounds. 15 compounds were common to both oils. oil A of H. tuberculatum exhibited antitumor activities against. liver carcinoma cell line (HEPG2) and lung carcinoma cell line (H1299) 4.7 µg/ml and 4.1 µg/ml. Conclusion: Essential oil of the aerial parts of H. tuberculatum is potentially active against lung (H-1299), and liver (HEPG2) carcinoma cell lines. The observed cytotoxic, activities can be attributed to the dominance of α and γ-terpinene in this oil.