Hydrothermal liquefaction (HTL) is a promising technology for the conversion of wet biomass into liquid fuels. In this study, the hydrothermal co-liquefaction (HTCL) of Spirulina platensis and alpha-Cellulose for bio-oil production was investigated. The bio-oil yield of HTCL was increased significantly by blending alpha-Cellulose with low-lipid content microalgae of Spirulina platensis in the absence of any catalysts supplementary which reduces the processing cost. The results showed that bio-oil productivity was increased drastically up to 4033 wt % (28.53 wt % with pure Spirulina platensis and 14.47 wt % with pure alpha-Cellulose), with a positive synergistic effect (SE) of 16 wt % during the HTCL process. The composition of synthesized bio-oil was analyzed by GC-MS which revealed that HTCL of Spirulina platensis and alpha-Cellulose are to decrease of its heterocyclic compounds, increased esters and hydrocarbons contents than HTL of pure Spirulina platensis or alpha-Cellulose. The possible reaction pathways were derived by synthesized bio-oil composition. The maximum energy recovery rate 82% was obtained on HTCL process. The study concluded that, HTCL process is more favorable for the economic concern due to high convention of bio-oil efficiency. (C) 2019 Elsevier Ltd. All rights reserved.