The effect of 11-oxo-oleanlic acid [I] and its derivatives on carrageenin-induced edema in rat kind paw was investigated. The following derivatives were synthesized ; 11-oxo-oleanolic acid methylester [II] C_(31)H_(48)O₄ mp 196-198° was derived from [I] by methylation with CH₂N₂. 3-Oxo-oleanolic acid [III] C_(30)H_(46)O₃, mP 198-202° was obtained from oleanolic acid by CrO₃-pyridine oxidation. Oxidation of [III] by CrO₃-HAc produced 3,11-dioxooleanolic acid [IV] C_(30)H_(46)O₃, mp 268-270° VU (λ max) 252 ㎚ and 3,11-dioxo-oleanolic acid lactone [V] C_(30)H_(44)O₄, mp 265-267° as a by-product. [IV] showed strong competitive inhibition against corticoid-5β-reductase, K_i= 4. 2×10-qM, compared to 4. 6×10^(-4)M of [I]. The anti-inflammatory activities of 11-oxo-oleanolic acid derivatives were evaluated by rat kind paw carrageenin edema test after s.c, injection with 30㎎/㎏ doses. [I], [II], [IVY and [V] suppressed significantly the edema volumes by 63, 78, 70 and 66%, respectively, compared to 66% of hydrocortisone. The above results suggest that the replacement of OH group in C₃ position by ketone group increased the corticomimetic activity, but that the change on the steric structure in C and D rings by lactone formation reduced the activity increase. [II] showed the most powerful activities probably due to increased lipophilicity.