Euphorbia decaryi is a species of plant in the family Euphorbiaceae endemic to Madagascar. Its natural habitats are subtropical or tropical dry forests, subtropical or tropical dry shrubland, and rocky areas. It is threatened by habitat loss.
Euphorbia decaryi is a spreading, evergreen plant, under 6" in height, and blooming April–June. Flowers are chartreuse, yellow-green, yellow, or red; female flowers carry a three-part pistil over a three-part ovary, producing three or sometimes more seeds.