We consider the effect of the Earth gravitational attraction on nuclear reactions at very low energies. In particular, the Mott oscillation characteristic of scattering of two identical nuclei is found to be slightly but significantly modified. The effect discussed here is different but complementary to the COW effect in cold neutron interferometry. We take as an example 208Pb+208Pb. An angle precision of about 10-3 deg. is required to detect the effect.