The effects of two types of catalysts and the catalyst/feedstock ratio on the fractional composition and basic physical properties of the bio-oil were studied. Chlorella microalgae biomass was used as the feedstock. Zeolite ZSM-5 in the H-form and ZrO2/Al2O3 in the sulfate-form were used as the catalysts. Increasing the catalyst load was shown to have positive effects on the contents of gasoline and diesel fractions in the bio-oil, to reduce significantly its density and viscosity, and to lower slightly the total sulfur content.