Perovskite-spinel epitaxial nanocomposite thin films are commonly grown on single crystal perovskite substrates, but integration onto a Si substrate can greatly increase their usefulness in devices. Epitaxial BiFeO3-CoFe2O4 nanocomposites consisting of CoFe2O4 pillars in a BiFeO3 matrix are grown on (001) Si with two types of buffer layers: molecular beam epitaxy (MBE)-grown SrTiO3-coated Si and pulsed-laser-deposited (PLD) Sr(Ti0.65Fe0.35)O-3/CeO2/yttria-stabilized ZrO2/Si. The nanocomposite grows with the same crystallographic orientation and morphology as that observed on single crystal SrTiO3 when the buffered Si substrates are smooth, but roughness of the Sr(Ti0.65Fe0.35)O-3 promoted additional CoFe2O4 pillar orientations with 45 degrees rotation. The nanocomposites on MBE-buffered Si show very high magnetic anisotropy resulting from magnetoelastic effects, whereas the hysteresis of nanocomposites on PLD-buffered Si can be understood as a combination of the hysteresis of the Sr(Ti0.65Fe0.35)O-3 film and the CoFe2O4 pillars.