In this study, Subphthalocyanine (SubPc) and SubPc integrated TiO2 nanoparticles (SubPc- TiO2) were examined as theranostic agents. In vitro photodynamic therapy (PDT) efficiency of SubPc/SubPc-TiO2 and nuclear imaging potential of I-131 labeled SubPc/TiO2-SubPc were determined on hepatocellular carcinoma (HepG2), colorectal adenocarcinoma (HT29) and human healthy lung (WI38) cell lines. As a result, I-131-SubPc and I-131-SubPc-TiO2 have been identified as a nuclear imaging agent for liver cancer. Additionally, I-131-SubPc-TiO2 has been found to be promising for imaging colon tumors. According to the in vitro photodynamic therapy studies, SubPc and SubPc-TiO2 were determined suitable PDT agents for liver and colon tumors. These results suggest that SubPc: TiO2 might be a theranostic agent with both PDT and nuclear imaging potential.