Although many peptides have therapeutic effects against diverse disease, their short half-lives in vivo hurdle their application as drug candidates. To extend the short elimination half-lives of therapeutic peptides, we developed a novel delivery platform for therapeutic peptides using an anti-hapten antibody and its corresponding hapten. We selected cotinine because it is non-toxic, has a well-studied metabolism, and is physiologically absent. We conjugated WKYMVm-NH2, an anti-sepsis therapeutic peptide, to cotinine and showed that the conjugated peptide in complex with an anti-cotinine antibody has a significantly improved in vivo half-life while retaining its therapeutic efficacy. We suggest that this novel delivery platform for therapeutic peptides will be very useful to develop effective peptide therapeutics.