Cocrystals of syndiotactic polystyrene (sPS) with polyethylene glycol (PEG) has been manufactured by using a guest exchange procedure to date. However, the guest exchange procedure is expected to be impractical for cocrystallization with high-molecular-weight PEG. This is because the higher the molecular weight of the guest PEG, the longer the time required for this procedure. To solve this problem, a new manufacturing process for sPS/PEG cocrystal film formation by casting a binary solute solution, has been developed. This simple procedure is applicable to even PEG with molecular weight of 20000.