In this study, a synthesis approach to pregabalin intermediate of isobutylsuccinonitrile(III) was proposed. Thus, III as well as 5-methyl-2-cyano-hex-2-enoic acid ethyl ester (I) and 2, 3-Dicyano-5-methyl-hexanoic acid ethyl ester (II) were synthesized from isovaleraldehyde and ethyl cyanacetate by three-step reaction of Knoevenagel Condensation, Cyano-addition and Decarboxylation. An 81.4% of overall yield was obtained by investigating molar ratio, temperature and reaction time to optimize the reaction conditions. The structures of the intermediates were characterized and confirmed by 1H NMR, IR and MS.