The problem of simultaneous phase separation and ordering kinetics in mixtures containing a nematic component is addressed through the introduction of a time-dependent Landau–Ginzburg model. Dynamic equations for the time evolution of orientation and concentration fluctuations are given; the solution to these equations leads to explicit expressions for the structure factors for concentration and orientation. It is shown that the theory shares some salient features with the Cahn theory of spinodal decomposition. A simulation of a quenching experiment is performed and the time evolution of the structure factors during spinodal decomposition is calculated. Relevant small angle light scattering experiments which could be used to test the model are discussed.