This study investigated the biological hydrolysis performance at 35 degrees C (BH35), 42 degrees C (BH42), and 55 degrees C (BH55) and the effect of temperatures on microbial communities of the hydrolyzed sludge. The results showed that the suspended solid reduction, volatile fatty acids (VFA) production, and biogas production increased with the BH temperatures. VFAs produced in the sludge BH included acetic acid, propionic acid, isobutyric acid, butyric acid, and isovaleric acid with the fractions of acetic acid increased with BH temperatures. The Illumina MiSeq sequencing analysis showed that the microbial taxonomic structures of the BH systems varied with BH temperatures. It was found that Acidaminobacter at 35 degrees C, Proteiniphilum and Lutispor at 42 degrees C, and Gelria at 55 degrees C were the main protein fermenting bacteria genera, while the carbohydrate fermenting bacteria might belong to the genera of Macellibacteroides and Paludibacter at 35 degrees C, Fronticella at 42 degrees C, and Tepidimicrobium at 55 degrees C.