Hydrothermal liquefaction (HTL) is a thermochemical processing technology for the conversion of waste biomass in the presence of water near critical condition. HTL is typically carried out between 250 and 350 °C and corresponding water-saturated pressures between 4 and 16 MPa, respectively. The process target product is a high viscous hydrophobic bio-oil called bio-crude. Bio-crude added value has been primarily recognized from bio-fuels perspective as a replacement for bio-diesel and bio-based aviation fuels, however, it can also upgraded into high added value products for the green chemistry and bio-based industries. The present study describes the design and set up of a new HTL experimental apparatus to investigate agro-waste biomass liquefaction at lab scale. The HTL apparatus was tested using tangerine peel waste and castor seeds as feedstock. Raw substrates, solid residues (hydrochars) and bio-oils were characterized in terms of proximate analysis and higher heating value while aqueous liquid residues were analyzed in terms of pH and total organic carbon content (TOC). Preliminary results obtained confirmed that the lab scale HTL apparatus, developed in this work, represents a valuable tool for the study of waste biomass conversion into high-energy dense solid and liquid bio-fuels.