The dielectric response (permittivity and losses) of epitaxial CoFe2O4–BaTiO3 thin film nanocomposites deposited under different conditions has been measured. Exhaustive microstructural analyses have allowed tracking the evolution of structure and morphology as a function of thickness, deposition temperature and rate. It is found that the dielectric permittivity of the nanocomposite increases with the grain size of the BaTiO3 matrix and when reducing its unit cell volume, while losses are quite insensitive to changes in morphology and crystal structure of the ferroelectric phase. We analyze the consequences of these results in view of the functional optimization of nanocomposites.