Mass transport in a nonisothermal binary molecular mixture is systematically discussed in terms of nonequilibrium thermodynamics, which for the first time allows a consistent and unambiguous description of the process. The thermodyanmic and hydrodynamic approaches are compared, revealing that nonequilibrium thermodynamics and physicochemcial hydrodynamics yield essentially the same result for molecular systems. The applicability limits for the proposed version of the thermodynamic approach are determined for large particles.