This paper studies the impact of specimen size and fiber content on the flexural fatigue response of high-performance fiber-reinforced concrete (HPFRC). For this purpose, six series of prismatic specimens were fabricated, considering two sizes (75 × 75 × 300 mm and 150 × 150 × 600 mm) and three fiber contents (0.3%, 0.6% and 1%). Twelve specimens from each series were tested in flexural fatigue under the same relative stress levels. It was sought to explain the variations in fatigue response through the observation of the mesostructure. In particular, correlations were established between the fiber distribution and the fatigue strength of all series. The results reveal that the parameter that most influences the ultimate static bending strength (σult) is the fiber volume in the central region of the specimens (Vfib), with the orientation having a much lower weight. In contrast, the opposite is true for cyclic tests. Since the fatigue stress levels were calculated in relation to σult of each series, the influence of Vfib is negligible. In this case, a clear correlation between fiber orientation with the longitudinal axis and fatigue strength is observed. Specifically, the orientation factor ηX accurately predicts both the characteristic fatigue life and the rate at which damage progresses in the main macrocrack.
