The first total synthesis of thiobutacin, a butanoic acid with antifungal activity recently isolated from the culture broth of a soil actinomycete, Lechevalieria aerocolonigenes strain VK-A9, is described. The five-step procedure involves readily available and cheap starting materials and can easily be transposed to the large scale. Fungal growth inhibition of thiobutacin is mediated by the pH of the