The hydro-liquefaction of Dunaliella sauna over solid acid catalyst was examined under moderate conditions (200 degrees C, 2.0 MPa, 60 min). The significant increment of bio-oil yield was obtained over Ni/REHY catalyst, increasing about 20% compared without modified REHY. H(2)-temperature-programmed desorption (H(2)-TPD) and X-ray powder diffraction (XRD) demonstrated that Ni/REHY as bifunctional catalyst played roles in hydrogenation and cracking, and further achieved the deoxygenation and desulfurization of D. sauna under hydrogen gas. The oxygen and sulfur contents of bio-oils decreased relative to D. sauna, and the higher heating value (HHV) significantly increased to 30.11 MJ/kg. From gas chromatography/mass spectrometry (GC/MS), the dominant compounds of the bio-oils were found to be esters, glycerins. The qualities of bio-oils were greatly improved. Hydro-liquefaction was beneficial to the exploration of bio-oils from microalgae. (C) 2011 Elsevier Ltd. All rights reserved.