In ferroelectric tunnel junctions, the ferroelectric polarization state of the barrier influences the quantum-mechanical tunneling through the junction, resulting in tunnel electroresistance (TER). Here, we investigate tunnel electroresistance in Co/PbZr0.2Ti0.8O3/La0.7Sr0.3MnO3 tunnel junctions. The ferroelectric polarization in tunnel junctions with 1.2-1.6 nm (three to four unit cells) PbZr0.2Ti0.8O3 thickness and an area of 0.04 μm2 can be switched by about 1 V yielding a resistive ON/OFF-ratio of about 300 at 0.4 V. Combined piezoresponse force microscopy and electronic transport investigations of these junctions reveal that the transport mechanism is quantum tunneling and the resistive switching in these junctions is due only to ferroelectric switching.