A method for extracting antineoplastic component from Bupleurum scorzonerifolium applicable in treating cell proliferative disorder is proposed. The antineoplastic components of Bupleurum scorzonerifolium include at least a Y-butyolactone centred heterocyclic compound with a Z configuration or E configuration at its carbon 2(5) position, and molecules, such as Chaihulactone, Isochaihulactone, Chaihulactone analogues or derivatives containing in the heterocyclic compound. From results of cell and molecular biological studies, in vivo animal test, and histological study, it is found that antineoplastic components extracted from Bupleurum scorzonerifolium are effective in suppressing a variety of cancer cell growths, inhibiting telomerase activity, as well as effective in killing with high specificity Taxol-resistant tumor cells at later stage of chemical therapy, making the components a new choice for anti-cancer agent, anti-HIV agent, or synergistic agent.