Objective: Nanoparticle-based drug delivery systems have been outstanding in developing therapeutic agents in cancer treatment. Obvious advantages of this system are that they can reduce the toxicity of existing anticancer drugs and enhance the targeting power of newly-developed therapeutic drugs. In this study, we applied and validated the therapeutic efficacy of new nanoparticle in epithelial ovarian cancer. Materials and Methods: Cathepsin B, an enzyme overexpressed in various cancers and is recently developed as a selective diagnostic marker and therapeutic target, was selected. Our team developed carrier-free nanoparticles of cathepsin B-cleavable peptide (Phe-Arg-Arg-Gly; FRRG)-conjugated doxorubicin (DOX) prodrug (FRRG-DOX). In HeyA8 and normal cell lines, we performed confocal microscope to evaluate the intracellular distribution of doxorubicin (DOX) and FRRG-DOX and cell counting kit (CCK) to identify toxicity of each drug. We also performed in vivo biodistribution study, therapeutic efficiency, and toxicity analysis study of DOX and FRRG-DOX in HeyA8 cell line xenograft. Patient-derived xenograft with high grade serous type was established for identifying therapeutic power of FRRG-DOX. Results: We identified relatively high levels of Cathepsin B in HeyA8 and HeyA8-MDR cell lines. FRRG-DOX and DOX were expressed in intracellular nucleus in HeyA8 cell line and cytoplasm in normal cell line. Also, long-term administration of FRRG-DOX did not damage normal organs, while DOX had toxicity to normal organs in in vitro experiment. In HeyA8 cell line xenograft experiment, FRRG-DOX significantly accumulate more than 3-4 times in tumor tissue with little effect on normal tissue, and had similar anticancer efficacy compared with DOX. Also, FRRG-DOX group did not show any side effects (weight loss, spleen size reduction, intestinal damage, etc.) which were shown in the DOX group. In the PDX model, tumor weights more decreased in the FRRG-DOX group when compared to control group (p<0.05). However, even if the concentration is doubled, it could be seen that it does not affect the effectiveness. Conclusion: FRRG-DOX nanoparticles showed the potential as an excellent anticancer agent that can minimize toxicity to normal tissue and maximize therapeutic efficacy. Also, introduction of cancer nanomedicine using nanoparticle-based delivery systems could provide a solution in epithelial ovarian cancer treatment.