A novel starch derivative of 2,4-bis(3- sulfonic aniline ) -1,3,5- triazine -6- starch ether (BSTSS) containing sulfonic acid groups was prepared in dimethylsulfoxide (DMSO) using 2,4-bis(3- sulfonic aniline)-6-chloro-[1,3,5]-triazine (BSTS) as etherifying agent. Effect of reaction conditions on the preparation of BSTSS was studied in detail and the optimized conditions were proved as follows: n (BSTS) : n (AGU) = 0.4 : 1, n (NaOH) : n (AGU) = 0.6 : 1, reaction time 4 h. The structure of BSTSS was determined by IR and NMR and the molecular weight of the product was measured by GPC . Effect of pH on the solution viscosities was studied and the results showed that the BSTSS had good acid and base resistance.