AbstractCorn starch was depolymerized by gamma irradiation (cobalt 60, approximately 1.25 Mrads/h) to prepare reduced viscosity products for surface‐sizing paper. The general effects of irradiation were determined on the extent of starch degradation, as well as dispersion variables. Low levels of irradiation, 0.02 to 0.5 Mrad, had a profound influence on granule swelling and disruption at a pasting temperature of about 90°C as determined in a recording viscometer. Product properties are affected considerably by carbonyl and carboxyl groups even when introduced at levels below 1 mmol/100 g. Carbonyl groups impart alkali sensitivity that produces significant degradation during dissolution in stoichiometric quantities of alkali. Carboxyl groups in starch paper sizes are detrimental because they act as dispersants for fines and fillers in repulped paper. Apparently dispersion in alkali is the most effective way to utilize irradiated starches as surface‐sizing agents. Corn starch irradiated to 2 Mrads and dispersed in alkali improved paper properties as well as a high quality commercial pro