We have performed a detailed analysis of the low frequency 1/fnoise in  YBa2Cu3O7−&dgr;   and  Bi2Sr2CaCu2O8+xgrain boundary Josephson junctions (GBJs) fabricated on SrTiO3bicrystal substrates. The normalized fluctuation of the critical current, &dgr;Ic/Ic, and the normal resistance, &dgr;Rn/Rnwere found to be almost independent of temperature and the misorientation angle. Furthermore, the magnitude of the fluctuations is very similar for both high‐Tccuprates. Correlation experiments showed that the fluctuations ofIcandRnare anti‐correlated. Our analysis strongly suggests that the source of 1/fnoise in high‐Tcbicrystal GBJs are localized defect states in an insulating grain boundary barrier with fluctuating electron occupation. The effective charge trapping time within single traps was found to decay exponentially with increasing bias voltage. ©1995 American Institute of Physics.