The impact fatigue behavior of a vinylester resin was studied with a pendulum-type repeated-impact tester especially designed and fabricated for the determination of single-impact and repeated-impact strengths. A well-defined energy-endurance impact fatigue curve was obtained with a progressive endurance at values of the impact energy below the critical value, with the endurance limit sot at an energy level of 31 N mm, 17.4% of the single-impact energy. The nature of the crack propagation was investigated for a single impact as well as high, medium, and low impact energy levels with progressively longer endurance. The fracture characteristics varied with the impact energy imparted and the number of cycles endured. The rate of lip growth was high at the higher impact energy levels with a lower number of endurance cycles and low at the lower impact energy levels with longer endurance; the repeated impacts created large and small compressive zones through the bending of specimens with the development of long and short lips, respectively.