Microstructural observation was performed on an Fe-0.3wt.%Cu alloy using a cross-sectional method. The specimens were solution treated and aged at 893K for 22.5h, followed by proton irradiation up to a fluence of 3×1021H+/m2(0.2 dpa at a peak position) at 353K. A band of structure, 0.8μm wide, was observed in a region 6.5 μm beneath the irradiated surface. The band consisted of a high density of black spot damage, which average size and number density at the center of the band was determined to be 2.3nm and 2.2×1026/m3, respectively. Besides the black spot damage, a number of small structures (<3nm) were observed in the defect band at strong two beam condition, while precipitates having F.C.C structure with a lattice constant of 10.16A and large precipitates (>6nm) causing halo rings corresponding to F.C.C. copper were observed at the region in and around both sides of the band. Taking in account results of micro vickers hardness and positron life-time measurements in Fe-Cu alloys, radiation hardening observed in Fe-0.3wt.%Cu alloy is attributed mainly to the radiation damage structures, such as dislocation loops and microvoids. However, It is pointed out that interaction between copper and carbon plays an important role on the microstructural evolution under irradiation and the resultant hardening in Fe-C-Cu alloys.