Background: Plantago major has been reported to have anticancer and anti-inflammatory properties. However, its antiproliferative and anti-inflammatory mechanisms have not been fully elucidated. Moreover, which plant parts are more suitable as starting materials has not been explored. Objectives: To investigate the antiproliferative activity of P. major extracts against MCF-7, MDA-MB-231, HeLaS3, A549, and KB cancer cell lines as well as their effects on inflammatory cytokines (tumor necrosis factor [TNF]-a, interleukin [IL]-1β, IL-6, and interferon [IFN]-g) production by lipopolysaccharide (LPS)-stimulated THP-1 macrophages. Materials and Methods: The methanol and aqueous extracts of P. major from different plant parts and its chemical compounds, i.e., ursolic acid (UA), oleanolic acid (OA), and aucubin were tested in this experiment. Results: Methanol and aqueous extracts of P. major seeds exhibited the greatest antiproliferative activity. The methanol extracts of seeds also demonstrated the highest inhibition of TNF-a, IL-1β, IL-6, and IFN-g production. Interestingly, the roots, which were commonly discarded, exhibited comparable activities to those of leaves and petioles. Furthermore, UA exhibited stronger activities than OA and aucubin. Conclusions: The seeds are being proposed as the main source for further development of anticancer and anti-inflammatory products, whereas the roots could be included in the preparation of P. major derived products with respect to anti-inflammatory.