The objective of this research was to evaluate the effect of the hydrothermal pretreatment on the solubilization of source separated organics (SSO) as well as the biomethane recovery through the mesophilic batch anaerobic digestion process. For this purpose, the SSO was subjected to fifteen different pretreatment conditions within five different severity index (SI) values (3, 3.5, 4, 4.5, and 5). The pretreatment temperature, holding time, and pressure ranged from 150 to 240 degrees C, 5 to 30 min, and 476 to 3367 kPa, respectively. The highest solubilization improvement of similar to 50% was achieved under the pretreatment condition of "220 degrees C-10 min-2323 kPa" corresponding to the SI value of 4.5. However, the maximum biomethane production yield of 280 mL/g TCODadded and biomethane production rate of 30 mL/g TCODadded were obtained under the less intense pretreatment conditions of "190 degrees C-20 min-1247 kPa" and "170 degrees C-30 min-786 kPa", respectively.