Toxins have been important tools to characterize the structures and functions of K+ channels in recent years due to their unique blockage of the K+ current and other physiological functions to the K+ channels, especially the voltage-gated K+ channels. Knowledge of the interacting surfaces between the toxins and the channels has been accumulated both from biological explorations and theoretical simulations. It has been found that the electrostatic potentials act as the driving force for the recognition of the toxins with the channels, and the orientation of the toxins over the channels follows the direction of the dipole moment. The binding site is composed most of the conservative residues of the negatively charged rings of Asp/Glu and residues around the edge of the central pore. The selectivity mainly comes from the type and distribution of the positive charged residues, and the whole topologies of the toxins. Based on the molecular determinants of the complex formation, and taking advantage of the structure-based methodologies of molecular design, it is hopefully to develop new generation of lead compounds specifically binding with subtypes of K+ channels.