[en] As tests on creep of the austenitic steel 03Cr20Ni45Mo4NbBZr on 873-973 K temperature interval showed some anomalies took place on creep curves, when before a non-steady stage of creep there was a section, on which the sample deformation didn't increase, but for some cases decreased with time. For instance, under neutron irradiation at temperature of 873 K and tensions of 296 or 302 MPa the sample deformation was not observed for initial 10 h. After this period of time the creep curves behaved as standard type ones and respectively for 400 h and 810 h became conventional. Decreasing of tension down to 178 MPa resulted in the section of non-changed in value strain reached 230 h. At equal temperature and tension rising of neutron flux density leaded to more clear appearance of the negative creep. The phenomenon of the negative creep was further investigated on non-irradiated aluminium alloy D16