Application of welded steel bar mesh is suggested for rational and labor saving construction of RC(reinforced concrete) caissons for port structures. It is usually pointed out that fatigue strength of steel bars is decreased due to thermal effect if steel bars are welded to each other, therefore welded steel bars are only used for limited cases in construction. Thus we compared the fatigue properties of three types of RC beams having different methods of connection of steel bars. The methods were two types of welding and a common connection method with wiring. We also studied the fatigue properties of RC beams with various arrangements of longitudinal steel bars. As a result of the study the fatigue strength of the beams with welded steel bars mesh was considerably smaller than that of common beams, especially when arc welding was used rather than resistance welding. However it was confirmed that those beams had strength of more than the design fatigue strength considering the effect of welding by 50% reduction in the standard specification for concrete structures by JSCE. Besides fatigue strength did not significantly decrease when longitudinal bars were overlapped with lateral spacing.