In this study, biogas production was investigated from cattle manure (CM), corn silage (CS) and sugar beet pulp (SBP) mixtures under mesophilic conditions. In anaerobic digestion (AD), CM, CS and SBP were mixed in different ratios and the optimum mixture ratio was determined as 2:1:1, w/w/w respectively. In this mixture, biogas production was 180.5 mL/g TS. After the optimum mixing ratios of CM, CS and SBP were determined, thermal pretreatments were applied to this mixture ratio. Thermal pretreatments were performed at 100, 120, 150 and 180 degrees C with 10, 20, 30, 60 and 120 min for each temperature. Considering biogas production after thermal pretreatment, the best thermal pretreatment time was determined as 60 min for all pretreatment temperatures. The highest biogas yield was 362.1 mL/g TS in the reactor which is pretreated at 180 degrees C for 60 min. After thermal pretreatment at 180 degrees C for 60 min, the SCOD value in the reactor increased by 124.6% compared to the control. This reactor produced 100.6% higher biogas production compared to the control. In addition, the solubilization of cellulose, hemicellulose and lignin in this reactor was 38.2%, 32.9% and 23.2%, respectively. Cumulative biogas production (CBP) fitted to modified Gompertz and modified Bertalanffy models.