Silica nanoparticles (SNPs) doped by hexanuclear molybdenum cluster complexes [{Mo6X8}L6]n (X = Cl, Br, or I; L = various inorganic or organic ligands) have been recently suggested as materials with high potential for biomedical applications due to both their outstanding photoluminescence properties and their ability to efficiently generate singlet oxygen upon photoirradiation. However, no studies were undertaken so far to prove this concept. Therefore, here we examined the potential of photoluminescent SNPs doped by {Mo6I8}4+ for applications such as bioimaging and photodynamic therapy using the human epidermoid larynx carcinoma (Hep-2) cell line as a model. Our results demonstrated both: (i) significant luminescence from cells with internalised molybdenum cluster-doped SNPs combined with the low cytotoxicity of particles in the darkness and (ii) significant cytotoxicity of the particles upon photoirradiation. Thus, this research provides strong experimental evidence for high potential of molybdenum-cluster-doped materials in biomedical applications such as optical bioimaging, biolabeling and photodynamic therapy.