Cycas armstrongii is a species of cycad in the genus Cycas, endemic to Northern Territory of Australia. It is found from the Finniss River in the west to the Arnhem Highway in the east, north of Pine Creek. It also occurs on the Tiwi Islands and the Cobourg Peninsula The female cones open, with 13–22 cm long sporophylls with 2-4 ovules per sporophyll on a lanceolate triangular lamina with an apical spine. The sarcotesta has a yellow coating when ripe. The male cones are ovoid, orange, 11–20 cm long and 7.5–10 cm diameter, with upper half of cone drawn to a point. Fruiting: March to September.