The microstructural evolution in ultra-fine grain (UFG) tungsten reinforced with ZrC particles under ion irradiation was investigated by transmission electron microscopy and compared to the effect of ion irradiation in reference ITER specification tungsten. Here, we report the evolution of the microstructure under heavy ion irradiation to mimic the neutron irradiation damage taking place in a nuclear fusion environment. The irradiation was performed with 9.1 MeV gold ions at 600°C to reach the end-of-life irradiation dose in ITER and DEMO divertor (i.e. 1 and 5 dpa). The microstructure is investigated by means of transmission electron microscopy. It is found that the ion induced defect structure does not deviate significantly from the reference tungsten. The main defects are a/2<111> type dislocation loops and nano-metric voids. The defect concentration is already saturated at 1 dpa and the higher irradiation damage was not found to have a significant effect on the defect concentration.