Investigations of comprehensive maintenance targeting 100-year-design life about a RC hollow slab bridge, which was damaged by salt contamination with use of initial chloride from sea sand and deicing salt, were conducted. The bridge was deteriorated seriously by reinforcement bars corrosion, cracks on concrete surface and exfoliations, and needed immediate repairing. It was clarified that removing of concrete 30mm deeper than rebar position and repair of cross section 55mm over thickness were necessary to the bridge by present conditions and prediction using neural network method.