The tautomeric equilibrium constant K-C of ethyl acetoacetate (EAA) in CO2-n-pentane and CO2-ethanol was studied by UV-VIS spectroscopy at 308.2 K over the pressure range from 6.5 to 9.0 MPa. This work focuses on how the tautomeric equilibrium changes with pressure and composition of the mixed solvents in the near critical region. The results showed that the effect of pressure on K-C was very limited at pressures much higher than the kinase separation pressures. However, the K-C increased sharply as the pressure approached the critical point or the bubble point of the mixed solvents.