Dioon is a genus in the family Zamiaceae. Species in this genus are dioecious and palm like shrubs. Many of them are chemically and biologically unexplored. The macroscopical and microscopical characters of three Dioon species that are cultivated in Egypt, D. holmgrenii De Luca, Sabato & Vázq.Torres, D. mejiae Standl. & L.O.Williams,  and D. meorlae De Luca, Sabato & Vázq. Torres were investigated. Their methanol extracts were biologically examined via cytotoxic activity against seven cell lines using MTT assay method, and antioxidant effects using bleomycin dependent DNA damage and ABTS antioxidant assay methods. The antimicrobial against Gram-positive, Gram-negative bacteria and fungi were also tested. Phenolic and flavonoid contents were analysed by Folin-Denis and aluminium chloride assays, respectively using gallic acid and rutin as standards. Results from this study revealed that there are some structural differences between the three species. D. holmgrenii and D. mejiae displayed high cytotoxic activity against number of tested cell lines, while D. meorlae showed less cytotoxicity. D. holmgrenii exhibited the highest antioxidant activity followed by D. mejiae then D. meorlae. Regarding the antimicrobial activity, D. holmgrenii was the most active species, particularly against Aspergillus flavus and Bacillus Subtilis followed by D. mejiae. Methanol extract of D. holmgrenii had the highest phenolic and flavonoid contents then D. mejia, while D. meorlae possessed the lowest contents.The two Dioon species, D. holmgrenii and D. mejiae displayed high biological activity.