Tricomponent system containing cellulose diacetate and the plasticizers mixture (triacetin and oligomer polypropylene glycol adipate) has been studied. isothermal cross-sections of the phase diagram obtained for five temperature in the 298-393 K range point out the existence of the upper consolute temperature. The dependence of T(g) of the system on the composition has been determined by the thermomechanical method and has the shape typical for the intrastructural molecular plasticization. The enthalpy of mixing of plasticizers and enthalpies of the interaction of their mixtures with cellulose diacetate have been measured by the calorimetry method. In systems with strong interaction of plasticizers the interaction with the polymer is weaker resulting in worsening of the plasticizing action. Enthalpies and Gibbs energies of mixing of the system components are calculated following the Flory-Patterson theory. An increase of the triacetin content in the mixture is accompanied by increase of the negative values of enthalpy and Gibbs energy of mixing with cellulose diacetate correlated with increase of the plasticizing action.