A solution-based approach has been developed for the synthesis of hollow or yolk-shell structured eta-Fe2O3 nanoparticles with versatile configurations via the Ostwald ripening process. By simply controlling the amount of PVP and reaction time in solution, hollow or yolk-shell structured eta-Fe2O3 nanoparticles with spherical, egg-like, olivary, elliptical, and shuttle-like configurations can be easily fabricated. The interior structures and morphologies of the particles are found to be effective ways to affect both the specific saturation magnetization and coercivity of the eta-Fe2O3 nanoparticles.