Various types of prismatic dislocation loops were produced by quenching in silicone oil of aluminum containing nominally 1 and 7 wt% magnesium, respectively. The annealing behavior of the loops was studied by transmission electron microscopy of thin foils of the quenched material. Direct experimental proof is given for the conversion of hexagonal perfect loops to diamond‐shaped loops, as well as for the rotation of perfect loops to different planes. The mechanism responsible for the coalescence of perfect loops is determined, and the nature of perfect loops evolving from climb sources is determined by their annealing behavior.