The positron annihilation measurements (CDB and positron lifetime measurement) and the electrical resistivity measurement were made for the isochronal annealing process of the Fe-Cu alloy specimens irradiated with electrons at low temperature. The peak in the high momentum region in CDB ratio curve grows prominently, showing the formation of Cu precipitates. W-parameter in the S-W plot already started to increase at 150K in Fe-0,6wt%Cu alloy specimens. The vacancy component I2 in the lifetime spectrum is kept almost constant beyond stage ID (110K) to about 300K, In the electrical resistivity measurement prominent recovery peaks appear at about 140K and 155K and these peak temperatures decrease with increasing Cu concentration. These results show that even at low temperature region below stage III self-interstitial atoms (SIAs) contribute to the formation of Cu precipitates through the mixed dumbbell mechanism and beyond stage III vacancies mainly contribute.