The present invention relates to a method for increasing the binding reversibility of a ω-conotoxin to a N-type calcium channel, which comprises preparing a ω-conotoxin having a Ile and/or Ala residue at a position of amino acid (11 and/or 12), respectively in the second loop between cysteine residues (2 and 3) of the ω-conotoxin represented by the formula I, such that the prepared ω-conotoxin has the increased binding reversibility to N-type calcium channel. In addition, the present invention relates to a novel ω-conotoxin and a pharmaceutical composition having plausible properties in view of blocking activity to and specificity to N-type calcium channel, and dramatically improved binding reversibility to N-type calcium channel.