Semisynthetic endothelin receptor antagonist S-0139 was synthesized in 14 steps from oleanolic acid 2 in a 20% overall yield on a multi-kilogram scale. Our previous synthesis of the oleanane skeleton was modified and improved to give phosphonate 9 as a key intermediate. The side chain on the 27-position was introduced by Horner-Wadsworth-Emmons olefination of phosphonate 9 with aldehyde 5. Aldehyde 5 was prepared in a one-pot reduction-acylation process starting from 5-hydroxy-2-nitrobenzaldehyde. The entire sequence of the synthesis can be done without chromatography and yields S-0139 of high purity.