The present invention relates to a formulation of polymer - drug conjugate with dual buffer system to minimize the cleavage between polymer and therapeutic drug. The present invention also relates to a method of preparation of stable pharmaceutically acceptable formulation of polymer - drug conjugates comprising use of two or more buffers which can stabilize the bonds or linkages between polymer and a therapeutic drug when present in solution form at elevated temperatures and repeated freeze-thaw cycles over a broad pH range. The present invention can also stabilize the lyophilized polymer - drug conjugates after reconstitution when stored in liquid form.
