In the present study, biodiesel produced by supercritical transesterification (non-catalytic) from Spirulina oil with alcohol (methanol and ethanol) was investigated. A factorial experimental design 2(2) with two central points for each alcohol was used. The effect of temperature (200 and 300 degrees C) and the amount of co-solvent (0.0005-0.003 g CO2/g methanol and 0.0003-0.001 g CO2/g ethanol) on the reaction yield was studied. Results showed that yield increased from 42% to 65% (at 200 degrees C) and from 46% to 72% (at 300 degrees C) when the amount of CO2 increased from 0.0005 to 0.003 g CO2/g methanol. By using CO2 as a co-solvent, it is possible to reduce the critical point of the reaction mixture (oil + alcohol) and thereby increase the reaction yield. For ethanolysis, the effect of selected variables was not statistically significant in the range of studied reaction conditions.