Aim: To gain insight into the interaction between the Charybdotoxin (ChTX) and BK channels. Methods: Site-directed mutagenesis was used to make two mutants: mSlo1-F266L and mSlo1-F266A. The two mutants were then expressed in Xeno-pus oocytes and their effects were tested on ChTX by electrophysiology experiments. Results: We demonstrate an equilibrium dissociation constant Kd= 3.1-4.2 nmol/L for both the mutants mSlo1-F266L and mSlo1-F266A similar to that of the wild-type mSlo1 Kd=3.9 nmol/L. Conclusion: The residue Phe266 does not play a crucial role in binding to ChTX, which is opposed to the result arising from the simulation of peptide-channel interaction.