The thermophilic (55 degrees C) hydrolysis and acidification were conducted in order to investigate the composition and distribution of proteins and polysaccharides and the effect of them on dewaterability of sludge. Sludge flocs were divided into four layers by centrifuge and ultrasound, i.e., slime, loosely bound-extracellular polymeric substances (LB-EPS), tightly bound-EPS (TB-EPS) and cells (Pellet). Results showed that most of proteins and polysaccharides located in pellet. Capillary suction time (CST) during digestion at pH 5.5 was slightly higher than the raw sludge, while CST during digestion at pH 10.0 was markedly higher than the raw sludge. Statistical analysis suggested that CST was affected by soluble proteins and soluble proteins/polysaccharides and virtually no affected by proteins, polysaccharides or proteins/polysaccharides in sludge and other layers except slime.