Corncobs is agricultural waste that have ascent amounts every years. The purposes of this research were to obtain information cellulose alternative source from corncobs for material of CMC; get optimum condition of synthesis CMC with food grade of DS and the characteristic of pH, viscosity, purity CMC. Synthesis CMC through alkalization and carboxymethylation process. The variation of NaOH concentration are 7,93; 10,00; 15,00; 20,00; 22,07% in alkalization and variations amount of NaMCA are 4,5858; 5,0000; 6,0000; 7,0000; 7,4142 gram in carboxymethylation. The result was cellulose content in corncobs is 62,80 %. The optimum condition which obtained from 15% NaOH and 5,04 g NaMCA gave CMC with DS 0, 82 ; pH 7,64 ; purity 99,52 % ; and viscosity 25,40 cps.