Kita- kyushu lung cancer antigen 1 (KK- LC- 1) is a kind of cancer- testis antigen with anti- tumor potential for clinical application. As a class of small- molecule antigen conjugate, tumor- targeting peptides have broad application prospects in gastric cancer diagnosis, imaging, and biological treatment. Here, we screened specific cyclic nonapeptides from a phage- display library. The targeting peptide with the best affinity was selected and further verified in ex vivo tissue sections. Finally, enrichment of targeting peptides in tumor tissues was observed in vivo, and the dynamic biodistribution process was also observed with micro- positron emission tomography (micro- PET)/computed tomography (CT) imaging. Studies showed that the specific cyclic nonapeptide had a high binding capacity for KK- LC- 1 protein. It has a strong affinity and specificity for KK- LC- 1- expressing positive tumor cells. Targeting peptides were significantly enriched at tumor sites in vivo, with very low normal tissue background. These findings demonstrated that the KK- LC- 1 targeting peptide has high clinical potential.