Required ultracentrifugal time for condensing a solution by ultracentrifuge with an angle rotor or a swing rotor was estimated by considering the calculated distribution of concentration in an ultracentrifugal tube. From the calculated distribution of the concentration a free boundary between solvent and solution was found in the ultracentrifugal tube under the condition that t*>0.25. A condense constant was newly defined as the ratio of the mean concentration in the ultracentrifugal tube after removing the solvent to the concentration of initial solution. The equation determining the required ultracentrifugal time for condensing a solution up to a given condense constant is derived and solved numerically. The required ultracentrifugal time for an angle rotor was shorter than that for a swing rotor.