Two　novel　axial-disubstituted　silicon(IV)　phthalocyanines　(compounds　1　and　2)　have　been　prepared　by　introducing　paracetamol　(a　common　antipyretic　analgesic)　or　its　isomer　4-hydroxyphenylacetamide　at　the　axial　positions　of　silicon(IV)　phthalocyanine,　respectively.　Their　photophysical　and　biological　properties　have　been　examined.　Both　compounds　are　highly　soluble　and　exhibit　very　similar　absorption　spectra　in　N,　N-dimethylformamide,　which　is　typical　for　non-aggregated　phthalocyanines.　Both　compounds　are　photocytotoxic　against　HT29　human　colon　adenocarcinoma　cells.　Compound　2　shows　a　very　high　in　vitro　photodynamic　activity,　with　the　IC50　value　down　to　15　nM.　In　contrast,　compound　1　exhibits　a　much　lower　in　vitro　photodynamic　activity　toward　HT29　cells,　which　can　be　attributed　to　its　higher　aggregating　trend　in　the　biological　medium　and　lower　singlet　oxygen　quantum　yield.　©　2009　World　Scientific　Publishing　Company.