The invention relates to a method for the modification of starch in such a way that it is suitable for surface sizing at high dry matter contents of >15%, typically >20%, even more than 25%. The modification of starch comprises at least degradation and stabilisation of the starch, whereby the degradation of starch is carried out by means of a chemical treatment, such as hypochlorite oxidation or acid treatment, to such a degree of degradation at which the viscosity of the surface size prepared from the starch, calculated to a dry matter content of 10% and to a temperature of 60.degree. C., still is at >5 mPas, typically >15 mPas, most typically >25 mPas, Brookfield RVTD II 100 rpm. The invention also relates to a starch intended for use in surface sizing at a high dry matter content and its use in surface sizing.