[reaction: see text] The asymmetric total synthesis of bacillariolide III has been achieved via 15 linear steps in 14.6% overall yield. The key feature of this synthetic route involves the highly stereoselective construction of the vinyl-substituted bicyclic lactone by an intramolecular Pd(0)-catalyzed allylic alkylation and its facile conversion to the hydroxy bicyclic lactone skeleton of bacillariolide III, induced by stereoselective vinylcerium addition to the aldehyde. In addition, the (Z)-pentenoic acid was efficiently introduced by the internal hydroxy group tethered ring-closing metathesis (RCM).