Euphorbia sieboldiana, the Siebold's spurge, is a species of flowering plant in the spurge family Euphorbiaceae. It is native to eastern Asia, where it is found in China, Japan, Korea, and eastern Russia. Its natural habitat is in grassy areas and forest margins. It is a common species in Japan. It is an rhizomatous perennial growing to 70 cm tall. It produces small flowers in compact pseudoumbels. These lack petal-like appendages. This species can be readily identified by the horn-like projections on the glands of the involucre. Blooming time is in spring and early summer.