Breast cancer is the second most common cancer worldwide with 1.68 million new cases and 522,000 deaths in 2012. Medical imaging-based diagnosis could help identify breast cancers at early stages, and substantially reduce mortality rate by providing early curative treatment. The advent of positron emission tomography (PET) has provided superior sensitivity and resolution compared to other imaging techniques, such as magnetic resonance imaging (MRI) and X-ray computed tomography (CT). Current PET diagnostic imaging methods rely on the high metabolism of tumor cells, and the tumors with similar metabolic rate to normal cells cannot be distinguished and are thus excluded from detection. Recent evidence suggested that neuropeptide Y1 receptor (Y1R) is overexpressed in a large portion of breast cancers, targeting Y1R with radiolabeled peptide probes for PET imaging would overcome the shortcomings of existing metabolism-based methods. This would in turn improve the detection rate of early breast cancer. One limiting factor with current peptide-based imaging probes is that the low stability of the peptides in serum that prevents them from reaching their target to provide an imaging signal. The purpose of this project was to develop novel imaging probes derived from known peptide sequences targeting Y1R, to improve their stability while improving/maintaining their target binding affinity. Our research showed that the novel peptide ligand, CCZ01035, exhibited excellent plasma stability and good binding affinity in vitro. 68Ga-labeled CCZ01035 selectively bound Y1R in vivo and produced high contrast PET images of Y1R positive tumor xenografts in mice. Our results suggest that [68Ga]CCZ01035 is a promising tracer for PET imaging of Y1R overexpressed breast tumors. The introduction of novel radiotracers for Y1R with PET imaging would allow early detection of breast cancers, which in turn would enable personalized curative treatment, and improve patient outcome.