Protein tyrosine kinase 7 (PTK7), a receptor found in tumor-initiating cells, is expressed in various malignancies, including ovarian cancer. Whereas PTK7 has been explored as a target for antibody-drug conjugates, this study is the first to investigate its potential for targeted radionuclide therapy. We developed a murine monoclonal IgG1 antibody (mOI-1) using hybridoma technology and generated a chimeric version (chOI-1) with human IgG1 constant regions. A cell-based screening approach using a library of 6,100 cell surface proteins identified PTK7 as the target, confirmed by flow cytometry and surface plasmon resonance analyses. IHC showed strong PTK7 expression in ovarian cancer tissues, and in vitro studies demonstrated specific binding and internalization of OI-1 in the ovarian cancer cell line SKOV-3-luc. Biodistribution studies using 177Lu-DOTA-mOI-1 injected intravenously in xenograft mice with subcutaneous SKOV-3-luc revealed high tumor uptake and retention. Therapeutic efficacy was assessed by intraperitoneal treatment with 212Pb-TCMC-chOI-1 in an intraperitoneal xenograft model, showing significant tumor growth inhibition compared with nonradioactive controls. This study provides the first investigation of a PTK7-targeting antibody (OI-1) as an antibody-radionuclide conjugate (212Pb-labeled) in a preclinical model of intraperitoneal ovarian cancer. These results support further investigation of OI-1 as a candidate for targeted radionuclide therapy in PTK7-expressing cancers.