Gold nanoclusters (GNCs) attract increasing attention due to their potential applications in sensing, catalysis, optoelectronics, and biomedicine. Herein, the formation of highly fluorescent glutathione (GSH)-capped GNCs is achieved through the delicate control of the reduction kinetics and thermodynamic selection of the Au(I)-SG complexes. Furthermore, the GNCs-based nanoprobes are developed by the covalent coupling folic acid (FA) and PEG (polyethylene glycol) on the surface of GNCs directly, followed by trapping photosensitizer (chlorin e6, Ce6) within PEG networks and attaching to the GNCs surface. The fabricated nanoprobes (Ce6@GNCs-PEG(2K)-FA) possess a uniform particle size (hydrodynamic diameter approximate to 6.1 +/- 1.2 nm), without affecting the yield of singlet oxygen of the trapped Ce6. In vitro studies show the enhanced cellular uptake and satisfactory photodynamic therapy (PDT) effectiveness toward MGC-803 cells when compared with free Ce6. The biodistribution and excretion pathway studies of the nanoprobes in MGC-803 tumor-bearing nude mice reveal their superior penetration and retention behavior in tumors, while the preserved features of renal clearance and stealthy to reticulo-endothelial system are mainly attributed to the small hydrodynamic diameters and the FA-capped PEGylated ligands. The enhanced PDT efficacy and the nontoxicity to mice provide an exciting new nano-platform with promising clinical translational potential.