New A-ring or/and C-ring modified methyl oleanolate derivatives were prepared. New simple method of synthesis of 3,12-diketone (3) from methyl oleanonate (2) was worked out. The obtained new compounds were tested for cytotoxic activity on KB, MCF-7 and HeLa cell lines. The derivatives had acetoxy, oxo or hydroxyimino function at the C-3 position and in some cases oxo, hydroxyimino or acyloxyimino group at the C-12 position. Almost all of the compounds showed strong cytotoxic activity, higher than unchanged oleanolic acid. The most active substances turned out to be the derivatives with acyloxyimino function, especially 4 and 8d.