In this study, [111In]In‐DOTA‐PR81 was developed, and its preliminary preclinical qualifications were assessed for single photon emission computed tomography (SPECT) imaging of breast cancer. DOTA‐NHS‐ester was practiced and successively purified by molecular filtration. The chelate:mAb ratio was determined by spectrophotometry. DOTA‐PR81 was radiolabeled with In‐111 and its radiochemical yield, in vitro stability, in vitro internalization, and immunoreactivity tests were performed. SPECT imaging and tissue counting were applied to evaluate the tissue distribution of [111In]In‐DOTA‐hIgG and [111In]In‐DOTA‐PR81 in BALB/c mice bearing breast tumors. The radiochemical yield of [111In]In‐DOTA‐PR81 complex was >95.0 ± 0.5% (ITLC), and the specific activity was 170 ± 44 MBq/mg. Conjugation reaction resulted in the average number of chelators attached to a mAb (c/a) of 3.4 ± 0.3:1. The radioimmunoconjugate showed immunoreactivity towards MCF7 cell line and MUC1 antigen while its significant in vitro and in vivo stability were investigated over 48 h, respectively (93.0 ± 1.2% in phosphate‐buffered saline (PBS) and 84.0 ± 1.3% in human serum). The peak concentration of internalized activity of [111In]In‐DOTA‐PR81 was between 4 to 6 h. In comparison with control probes, the complex was accumulated with high specificity and sensitivity at the tumor site. Achieved results indicated that [111In]In‐DOTA‐PR81 could be contemplated as an appropriate radiotracer for prognostic imaging of antigens in oncology.