A convenient stereoselective synthesis of 16-hydroxy-9Z, 12Z, 14E-octadecatrienoic acid (1), 9-hydroxy-10E, 12Z, 15Z-octadecatrienoic acid (2), 9-hydroxy-10E-octadecenoic acid (3) and 10-hydroxy-8E-octadecenoic acid (4), the four self defensive substances in rice plant and timothy plant are described.