To optimize the preparation conditions of carboxymethyl potato starch (CMPS), the effects of relevant factors on viscosity (eta) of 2% CMPS aqueous solution and degree Of substitution (DS) were investigated. These condition parameters included etherification temperature, alkalization and etherification time, water content in the mixed solvent, ratio of liquid volume to starch mass, molar ratio Of sodium hydroxide to monochloroacetic acid, and molar ratio of monochloroacetic acid to anhydroglucose unit. After individual parameter influencing eta and DS was researched one by one, an Orthogonal experiment of L-18 (2 x 37) was designed to identify the main factors affecting them. In light of range analysis, the comparative importance of factors impacting eta and DS was obtained, separately. Results of variance analysis showed that the most effective factor to control DS vas etherification temperature, whereas the influences of all factors on eta were not significant. Meanwhile, eta and DS of the optimized final product were found to be 12,000 mPa.s and 0.68, respectively. In addition, the Structure of CMPS was characterized by Fourier transfom-1 infrared (FTIR) spectrophotometer. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 24-33, 2009