The poor water-solubility and instability of Ru(II) carbonyl complex hamper the therapeutic application as CO releasing materials (CO-RMs). To enhance the hydrophilicity and bio-utility of CO, a robust Ru(I) carbonyl sawhorse skeleton were grafted with water-soluble PEGlyated sidearms. Twelve PEGlyted sawhorse Ru2(CO)4 complexes were prepared with satisfactory yields and characterized by IR and 1H- and 13C- NMR. X-ray diffraction analysis of CO-RM 8, 13 and 14 revealed the featured diruthenium sawhorse skeleton and PEGylated axial ligands. The flask-shaking method measures the hydrophilicity of CO-RMs, indicating that both bridging carboxylate ligand and PEGlyated axial ligands regulate the hydrophilicity of these CO-RMs. Under photolysis conditions, CO-RM 4-13 sustainable released therapeutic amounts of CO in myoglobin assay. The correlation of the CO release kinetics and hydrophilicity of CO-RMs demonstrated that the more hydrophilic CO-RM released CO faster. The biological test found the low cytotoxic CO-RM 4 showed a specific anticancer activity toward HT-29 tumour cells.