Starch matrix in the air- and oven-dried states was compreseed under 0,8-1,2 x 10⁹ Pa. Depolymerization of starch with slight hydrolysis is noted at 0,8 and 1,2 x 10⁹ Pa whereas some repolymerization takes place on compression under 1,0 x 10⁹ Pa. Amylopeetin is the component of starch matrix which suffers most damage under experimental conditions. Starch additionally moisturized and with severl mineral salts as additives does not suffer deep changes. The effect of salt on the course of thermal decomposition is noted it is practically independent of the pressure applied to such starch - additive mixtures.