This study investigates the effects of catalyst preparation techniques on the yield and quality of liquid biofuel produced from slow catalytic pyrolysis of microalgae Chlorella sp. using various catalysts, including acid catalysts (HZSM-5) and base catalysts (activated carbon). The effects of different temperatures, catalyst loading, and reaction time on the yield and quality of liquid biofuels, including chemical composition, density, and the resulting viscosity at the optimal variable, were investigated. The results showed that slow catalytic pyrolysis using 1 wt.% activated carbon catalyst, a temperature of 550°C, and a reaction time of three hours produced a maximum yield of liquid biofuel at 50.38 wt.% with high aromatic hydrocarbons, less oxygen and acid, a density of 0.88 kg/L, and a viscosity of 5.79 cSt that satisfied specifications of biodiesel No. 2. Slow catalytic pyrolysis with a variety of catalyst types and catalyst preparation techniques affects the increase in yield and quality adjustment of liquid biofuel. The proposed technology can be further developed for commercial applications, replacing conventional diesel fuel.