Tin(IV) complexes of a 4-methylthiophenyl functionalized porphyrin (1-Sn) and its corrole analogue (2-Sn) were synthesized so that their photophysicochemical properties and photodynamic activities against MCF-7 breast cancer cells could be compared. Singlet oxygen luminescence studies revealed that 1-Sn and 2-Sn have comparable φvalues in DMF of 0.59 and 0.60, respectively, while the IC50 values after irradiation of MCF-7 cells for 30 min with a Thorlabs 625 nm LED (432 J · cm-2) were determined to be 12.4 and 8.9 μM. The results demonstrate that the cellular uptake of 2-Sn and its molar absorptivity at the irradiation wavelength play a crucial role during in vitro cytotoxicity studies.