Corrosion protection for prestressing steel materials used for prestressed and post-tensioned structures is one of the most important factors needed to increase the structure service life. The corrosion protection is usually applied at the construction site by cement grouting or other means, however, it has been discussed for several years that it is sometimes difficult to control the protection quality due to operator's skill variation, grout quality, weather or other factors. On the other hand, several prestressing materials with factory applied corrosion protection have been used in various applications, such as prestressing, post-tensioning, stay cables and ground anchors. In general, this type of prestressing material has several corrosion protection layers around the steel and has the following advantages: a. highly reliable corrosion protection due to quality controlled manufacturing processes. The quality can be also maintained after production in the plant, during delivery, during construction and during the structure service life;b.labor cost saving and rapid construction by eliminating corrosion protection work on site; c. Easier inspection and replacement of cables in the future. Epoxy coated and filled prestressing steel strand (ECS) is one of the most common materials produced with a factory-applied corrosion protection. This material is perfectly protected by epoxy coating on both the outside and inside of the steel strand. It has been applied to various PC bridges since 1983 such as cable stayed bridges, extra-dosed bridge and box girder bridges. This paper will introduce several evaluations conducted using ECS in order to verify that ECS performs sufficiently enough to maintain long service life of PC bridges