In the present study, a microalga (Chlorella pyrenoidosa) was treated in sub/supercritical acetone in the absence of catalyst by using a high pressure bath reactor. Influence of process variables such as temperature (varied from 170 to 350 degrees C), acetone/microalga ratio (varied from 2/2.5 to 16/2.5), and time (varied from 5 to 120 min) on the yields of product factions and properties of biocrude has been studied. Temperature was the most influential factor affecting the products yield and properties of the biocrude, and the highest biocrude yield of 60.1 wt.% was achieved at 290 degrees C. Addition of acetone not only promoted the conversion of microalga but also favored the biocrude yield due to the incorporation of acetone into the biocrude. Furthermore, liquefaction of microalga in acetone made the conversion milder that than of in water. The biocrude was less viscous than that of oil produced from hydrothermal liquefaction under otherwise identical reaction conditions. The biocrudes, which contained significant carbon and hydrogen than that of the original algal biomass, had higher heating values ranging from 28.7 to 37.1 MJ/kg. The most abundant compounds for the biocrude are unsaturated fatty acids (9,12,15-octadecatrienoic acid) and hydrocarbons (2-hexadecene, 3,7,11,15-tetramethyl-). CO2 was the dominant component in the gaseous products under all experimental conditions. Deoxygenation and denitrogenation are necessary if one to expect to produce transportation fuels from this kind of biocrude. (C) 2014 Elsevier B.V. All rights reserved.