IntroductionCancer, one of the leading causes of human death, has attracted more attention due to the complexity of etiology, diagnosis and treatment [1]. In recent years, chemotherapeutic management against various types of cancer including leukemia has been increased rapidly though some times cancer cells resistance against chemotherapy [2,3]. In this respect, search for effective anticancer agent that inhibit the proliferation of the cells as well as inhibit the resistance nature of the cancer cells and induce differentiation of the monocytes is an ongoing challenge. Therefore to find out anticancer agent with multi-target efficacies, attention has been focused on plant products as the plant products have been used as remedies for several human diseases including cancer from ancient times with lower side effects [4]. The reasons for using them that they contain variety of chemical compounds usually secondary metabolites with therapeutic values [5]. Cestrum parqui is belonging to the family Solanaceae, usually known as "green or Chilean cestrum" in Tunisia, are rich in various secondary metabolites such as saponins, polyhydroxylated terpenes (C13 norisoprenoids, sesquiterpenes, spirostanes and pseudosapogenins) and ent-kaurene glycosides (parquin and carboxyparquin) [6][7][8]. Several scientific reports demonstrate that C. parqui exhibits a wide spectrum of pharmacological activity when administered systemically or in isolated organ preparations. For example, it is used to treat headache, rheumatic pain, scabies, dermatosis, diarrhaea and metrorraghia [7]. The plant is also used in Chilean folk Abstract Background: In our time, there is an urgent need to discover natural anticancer products without toxic side's effects. Objective: The present study was conducted to investigate the anticancer activity of the methanolic extract of Cestrum parqui leaves as well as identification of the active compounds in this concern. Materials and Methods: Eight column chromatographic fractions were tested against human leukaemia cell line (HL-60) and the cell viability was measured by dimethylthiazol tetrazolium assay. Studies of apoptosis, cell cycle and DNA fragmentation were carried out following the standard protocol. Effective fractions were analysed by high performance liquid chromatography-ultra violet, HPLC-evaporative light scattering detector and preparative-HPLC. Finally the active compounds were identified by gas chromatography coupled to mass spectrometry. Results: Out of eight, fraction II showed remarkable inhibition on the growth of HL-60 cell line and fraction I showed moderate activity on such inhibition. Mechanisms of the inhibition were identified as cell cycle arrestation and apoptosis induction by the said fractions. Chromatographic and mass spectrometric analysis of the fraction II indicated the presence of oleanolic and ursolic acids as biologically active compounds. Conclusion: This study is the first investigation that shows Cestrum parqui has anticancer activity and the responsible compounds are olea...