A new method of stereos, elective synthesis of 0c-(1-4) linked thiodisaccharides: 4-S-(o~-L-fucopyranosyl)-4-thio-3-deoxy-ot-D-glucopyranose 6 and 2-acetamido-2,3 dideoxy-4-tbio-(et-L-fucopyranosyl)-4-thio-0c-D-glucopyranose 7, by Michael addition of 1-thio-~-L-fucopyranoside to levoglucosenone is described. The inhibition study of 6 and 7, against ot-L-fucosidase (from bovine kidney) indicates the importance of 3-deoxy position of glucosamine moiety for total inhibitory effect Ki=4.0mM and K~=2.4mM respectivelly.