Tri-tert-butyl-carboxyl subphthalocyanine (SubPc) was synthesized and evaluated as a fluorescence agent. Fluorescence imaging for breast tumor in vivo was performed using nude mice as models. Results indicate high uptake in tumor at 20 h. Tumor-non tumor ratio was determined as 2.25. The imaging results demonstrate the potential of this fluorescence-imaging agent in the diagnosis of breast tumor. In the future, subphthalocyanine is also developing as a dual functional, which is fluorescence imaging and as a photodynamic therapeutic agent for the treatment and diagnosis of cancer.