Compared to conventional concrete, Ultra High Performance Concrete (UHPC) has high tensile strength and ductility that result from the steel fiber bridging effect across cracks. However, since its tensile behavior depends largely on fiber orientation, it is required to understand the effect of fiber orientation on the tensile and accordingly structural behavior to apply UHPC to a structural design. This study reports the flexural behavior of UHPC prestressed T-girders and the estimation of the effect of steel fiber orientation on their flexural behavior. To easily reflect this effect in the design, this paper estimates the correction factor K defined as the ratio of the tensile strength of a prism specimen to that of a target structure. The flexural test shows that, at the peak load carried by the girder, the steel fibers at one specific cross section begin to pull out. This crack width becomes significantly wider than any other cracks in the girder. Eventually, the fibers bridging the highly stressed crack begin to pull out. Thereafter, UHPC prestressed T girder is failed by the local bond failure between fibers and the UHPC matrix. The analysis of test results shows that prestressing tendons disturb the fiber orientation during the placing, and accordingly reduce the tensile strength of UHPC in the girder. The correction factor K in the present study is suggested 1.50-1.77.