Snake venoms are a mixture of pharmacologically active proteins and polypeptides that have led to the development of and therapeutic agents. Here, we describe the structural and functional characterization of a novel neurotoxin, haditoxin, from the venom of Ophiophagus hannah (King cobra). Haditoxin exhibited novel pharmacology with antagonism toward muscle (a߿d) and neuronal (a7, a3߲, and a4߲) nicotinic acetylcholine receptors (nAChRs) with highest affinity for a7-nAChRs. The high resolution (1.5 ũ crystal structure revealed haditoxin to be a homodimer, like ?-neurotoxins, which target neuronal a3߲- and a4߲-nAChRs. Interestingly however, the monomeric subunits of haditoxin were composed of a three-finger protein fold typical of curaremimetic short-chain a-neurotoxins. Biochemical studies confirmed that it existed as a non-covalent dimer species in solution. Its structural similarity to short-chain a-neurotoxins and ?-neurotoxins notwithstanding, haditoxin exhibited unique blockade of a7-nAChRs (IC50 180 nm), which is recognized by neither short-chain a-neurotoxins nor ?-neurotoxins. This is the first report of a dimeric short-chain a-neurotoxin interacting with neuronal a7-nAChRs as well as the first homodimeric three-finger toxin to interact with muscle nAChRs.