This paper discusses the effectiveness of cathodic protection for prestressed concrete structures under marine environment. Testing specimens were pre-stressed concrete beams fabricated by pre-tensioned method. All of them contained chloride ion, of 9kg-Cl- per volume. The experimental parameter is with or without cathodic protection. For protected specimens, anode material, which is titanium mesh, titanium bar, zinc sheet, or electric conductive paint, was affixed on surface of specimen. All of specimen has been exposed to splashing sea water for ten years. Then several tests ware conducted so as to discuss about flexural behavior of beam specimens, corroded condition of PC strand, mechanical property of corroded strand, chloride content of concrete, and residual.performance of anode materials.
　The following conclusion can be drawn in this study:
1) The protection methods, using titanium mesh, zinc sheet, and electric conductive paint, enable to prevent corrosion. Consequently the test result based on electrochemical method during exposure term prove the effectiveness of corrosion protection. Further corrosion products was a small amount when these method was applied.
2) The strand was corroded in the specimen protected by titanium bar, because electrochemical test result did not satisfy the specification for corrosion free. This material, as a result, is not suitable for anode rnaterial.
3) When the effective protection method was applied, the material properties of the strand was satisfied its own standard value.
4) When the effective protection method was applied, the nexural performance showed as same as non-corroded one. However, the flexural capacity with titanium bar, and without protection was about 35 % loss of non-corroded capacity.