In this study, liquefaction of Chlorella vulgaris biomass grown in photo-bioreactor using wastewater as source of nutrition was studied and influence of process parameters on the yield of bio-oil was analysed. Different biomass to water ratio (5 g/200 ml, 10 g/200 ml, 15 g/200 ml, and 20 g/200 ml) was taken and bio-oil yield at various temperatures ranging from 220 to 340 degrees C was studied. Catalyst loading of the range 2.5-8% wt of NaOH was also studied to analyse the influence of catalyst concentration on bio-oil yield. Obtained bio-oil was characterized using Gas Chromatography Mass Spectroscopy (GC-MS) and Fourier Transform Infrared Spectroscopy (FTIR). Results showed that maximum bio-oil yield of 26.67% wt was observed at operating conditions of 300 degrees C, 15 g/200 ml biomass load and 2.5% wt of NaOH at 60 min holding time. Fatty acids and other high carbon compounds were detected in the bio-oil obtained through liquefaction process.