The dried aerial parts of Euphorbia mongolica afforded three new acylated polyhydroxy diterpenoids based on the jatrophane framework. The structures were established by means of a combination of 1D and 2D NMR techniques and mass spectrometry as (2S,3S,4R,5R,7S,8R,13S,15R)-5alpha,7beta,8alpha-triacetoxy-3beta-benzoyloxy-15beta-hydroxyjatropha-6(17),11E-diene-9,14-dione (1), (2S,3S,4R,5R,7S,8S,9S13S,15R)-5alpha,7beta,8alpha,9alpha,15beta-pentaacetoxy-3beta-benzoyloxyjatropha-6(17),11E-dien-14-one (2), and (2S,3S,4R,5R,7S,8S,9S13S,15R)-3beta,7beta,8alpha,9alpha,15beta-pentaacetoxy-5alpha-benzoyloxyjatropha-6(17),11E-dien-14-one (3). When the isolates were assayed for multidrug resistance-reversing activity in a rhodamine 123 exclusion test using L5178 mouse lymphoma cells, all compounds demonstrated a concentration-dependent effect in inhibiting the efflux pump activity of these tumor cells in the range 11.2-112 microM.