The biological activity and toxicity of crude venom from Conus betulinus, which was collected from the South China Sea, were studied. The venom shows Ach receptor activity, K+ current effect, and low toxicity. Four peptide components, named BeTXIa, BeTXIb, BeTXIIa, and BeTXIIb, were purified by gel-filtration with Sephadex followed by HPLC, and finally sequenced on an ABI model 491 sequencer. The low-molecular-weight peptides BeTXIa and b have 14 and 15 amino acid residues, respectively, while BeTXIIa and b have 27 and 30 amino acid residues, respectively. The results indicate that BeTXs from the venom of C. betulinus are a set of small peptides with a high cysteine content like known conotoxins. However, it is meaningful to find that these sequences have specific chemical characteristics in their cysteine framework which differ greatly from known cysteine frameworks in conotoxin structures.