In these years, the PC use for port and harbour structures has become active, and it is necessary to get more information on durability of PC in marine enviroment.
　This paper reports the investigation on the three unanwered questions, namely, about the cover depth, new corrosion prevention methods, and the joints and ancho rages.
　The PC beam specimens include such factors, as the cover depth of the embedded steels, the method of tensioning, with or without corrosion prevension method, and with or without joint.
　After 7 years' exposure of the PC beams in marine environment, the observation of the corrosion states of the steels, the measurement of the chloride contents,
and the electrochemical measurements are made.
　The experimental results obtained so far are as follows; (1) The reduction of the cover depth of the embedded steels in the pre-tensioned PC members can't permitted from the viewpoint of corrosion prevention. (2) The epoxy coating on the PC beam is effective for corrosion prevention. (3) The epoxy resin joint is sufficient, but the protection of the anchorages isn't for corrosion protection.