A microscopic theory of the self-current correlation function is presented by deriving its memory function which consists of two parts. The first is the kinetic term whose time decay is expressed in terms of the velocity autocorrelation function and the self-intermediate scattering function. The second is the potential term which is expressed in terms of the interatomic potential, the radial distribution function, the self-intermediate scattering function and another quantity which describes collective effects in the liquid. For the wavenumber value k=0, this memory function is identical with the memory function of the velocity autocorrelation function which has been derived by Chiakwelu and Gaskell (1976). A preliminary calculation with liquid rubidium shows that the memory function is rapidly damped with increasing values of k. This latter behaviour is presumably due to the strong modulating effect of the self-intermediate scattering function.