Abstract Epitaxial YBaCuO films with critical current densities up to 5 ∗ 10 6 A/cm 2 at 77 K have been grown in-situ on different single crystalline substrates by excimer laser evaporation. Defects have been generated in these films by a too low oxygen pressure during the evaporation as well as by irradiation with 25 MeV 16 O ions and 173 MeV 129 Xe ions. A decrease of T c in correlation with an extension of the c-axis parameter is observed. The effects of the irradiation with the two projectiles differ dramatically as revealed by the T c reduction and the resistivity increase as function of the irradiation fluence.