Aluminum single crystals with a low dislocation density were grown by the strain-annealing method from ultrahigh-purity (UHP) materials. The crystals were annealed cyclically six times to decrease the dislocation density. The number density and the Burgers vector of the residual dislocations were examined by the X-ray Lang topography and the synchrotron radiation topography with white beam X-ray, respectively. The number density and the nature of the dislocations were 1 X 10(3) cm(-2) and 60degrees dislocations, respectively. These results were similar to those in the high-purity aluminum crystals. The cause of the results is attributed to the amount of residual vacancies after growth. The calculated residual vacancy concentration in crystal after slow cooling attains 1.2 x 10(-6), which is about ten times as large as the impurity concentration in UHP aluminum. So the residual vacancy concentration in the UHP aluminum hardly depends on the impurity concentration. It seems that the formation mechanism of dislocations by excess vacancies in UHP aluminum is similar to that in high-purity material because the amount of residual vacancies in both the crystals are nearly equivalent. (C) 2002 Elsevier Science B.V. All rights reserved.