Ultra-high toughness cementitious composite (UHTCC) is a PVA fiber reinforced cementitious composite. Tensile strain hardening behavior with ultimate tensile strain of more 3% under direct tensile loading is one of its important characteristics. In the current article, nine simply-supported reinforced UHTCC beams were subjected to four-point bending loading to experimentally investigate the influence of ductile deformation behavior of UHTCC on ductility capacity of reinforced structural members. Ductility index is determined by adopting three different parameters, i.e., deformation capacity, energy dissipation capacity as well as curvature capacity. The effect of longitudinal tensile reinforcement ratios on the variation of ductility in UHTCC reinforced beams was examined. It was found from the experimental results that the combination of ductile matrix (UHTCC) and steel bar prevents from occurrence of localized cracks in pure bending zone, showing high damage tolerance and ductile failure behavior. The results also show that as longitudinal tensile reinforcement ratio increases, deformation ductility and curvature ductility both exponentially decrease while a small reduction is demonstrated for energy ductility at ultimate failure.