The present work demonstrates the influence of experimental conditions such as weight ratio of sewage sludge to water (1/0–1/15), reaction temperature (200–350 °C), initial H2 pressure (2.0–11.0 MPa), residence time (10–100 min) and type of catalysts (Na2CO3, Raney nickel, FeSO4, MoS2) on hydro-liquefaction process of sewage sludge. High amount of water improves the hydro-liquefaction process of sewage sludge by increasing the yield of bio-oil and the total conversion. The highest yield of bio-oil (47.79 wt.%) from sewage sludge was obtained with initial H2 pressure 5.0 MPa, reaction temperature 300 °C, and residence time 40 min. Under these experimental conditions, using weight ratio of sewage sludge to water 1/5, catalyst (FeSO4) – 5 wt.% of dry SS, mixing speed 350 rpm the obtained bio-oil had the highest energy recovery (69.84%), total conversion (70.64%) and its calorific value was 35.22 MJ/kg.