Euphorbia neriifolia L. is a spiny herb native to Southeast Asia and currently cultivated in southern Taiwan. From the ethanolic extract of E. neriifolia leaves, 23 compounds were isolated, including 22 triterpenoids and one flavonoid glycoside. The anti-human coronavirus (HCoV) activity of the separated triterpenoids was studied revealing the structure-activity relationship (SAR) of these isolates. 3β-Friedelanol exhibited more potent anti-viral activity than the positive control, actinomycin D, which implies the importance of the friedelane skeleton as a potential scaffold for developing new anti-HCoV-229E drugs.