A series of novel silicon(IV) phthalocyanines conjugated axially with different nucleoside moieties (uridine, 5-methyluridine, cytidine, and 5-N-cytidine derivatives) have been synthesized and evaluated for their photodynamic activities. The uridine-containing compound 1 exhibits the highest photocytotoxicity against HepG2 human hepatocarcinoma cells with an IC50 value as low as 6 nM, which can be attributed to its high cellular uptake and non-aggregated nature in the biological media. This compound shows high affinity toward the mitochondria of HepG2 cells and causes cell death mainly through apoptosis upon illumination. The result indicates that 1 is a highly promising photosensitizer for photodynamic therapy.