The objective of this study was to investigate the impact of the hydrothermal pre-treatment (HTP) on solubilization and acidification of thickened waste activated sludge (TWAS) and source separated organics (SSO). The temperatures, retention times, and pressures used in this study ranges were 150-240°C, 5-30 min, and 69-488 psi, respectively. Mesophilic batch acidification tests were conducted for all pretreated and non-pretreated samples. For the TWAS, the highest overall COD solubilization due to HTP and acidification of 64% was observed at “200°C-10 min” compared to 30% for raw TWAS. The highest VFAs yield of 2856 mg VFAs/g VSS added was observed at “190°C-10 min” compared to 1251 for raw TWAS. For the SSO, the highest overall COD solubilization of 63% was observed at “210°C-20 min” compared to 17% for raw SSO. The highest VFAs yield of 1536 mg VFAs/g VSS added was observed at “210°C-20 min” compared to 768 for raw SSO.