Plant based treatments continue to play an essential roie in primary health care, and it has been estimated by the World Health Organization (WHO) that almost 65% of the world's inhabitants rely mainly of traditional medicines for their primary health care. Medicinal plants constitute important components of flora and widely distributed in Thailand. The pharmacological evaluation of substances is an established method for the identification of lead compounds which can lead to the development of novel and safe medicinal agents. Based on the literature, A number of plant species of medicinal plants used in traditional medicine in Thailand will be collected. The constituents of these plants will be screened for their cytotoxic activity.