Polymer concrete is a composite material that uses polymeric resin as aggregate filler. This type of concrete is strong, durable, non-absorbent and chemical resistant. Under cyclic loadings pre-existing cracks inside both conventional concrete and polymer concrete may grow and cause catastrophic failure of the structure. Structural failure under cyclic loading is also known as the fatigue failure. This study aims to investigate the behavior of plain and polymer concrete under the cyclic loading or fatigue. The specimens used for this study included cylindrical specimens of 3 inch diameter and 6 inch in length. They were subjected to compressive load for various numbers of cycles. The applied load was gradually increased. After the loadingunloading cycles, nonlinear impact resonance acoustic spectroscopy (NIRAS) test was carried out on the samples using instrumented impact hammer. The degree of nonlinearity in the concrete specimens was measured by recording the shift in the resonance frequency as the impact energy increased. The results indicated that for conventional concrete specimens the material nonlinearity increased with the number of loading cycles and the applied load magnitude. However, for polymer concrete it remained almost unchanged. Experimental results from conventional plain concrete and polymer concrete specimens were compared.