The behaviour of Kr atoms in aluminium has been investigated by an ion channelling method with a He+beam on Al specimens implanted at room temperature at 50 keV to various doses from 1 × 1014to 1 × 1016Kr/cm2. The Kr atoms are distributed over random (R), substitutional (S), tetrahedral (T) and octahedral (O) sites. From the implantation-dose dependence of the site occupancies, it is considered that, at the initial stage of implantation, Kr-vacancy (V) complexes such as KrV4and KrV6are formed and they act as nucleation centres for the subsequent growth to bubbles. KrV4and KrV6complexes are dissociated around 433 and 593 K, respectively. It is observed that post-implantation irradiation enhances the formation of solid krypton. On the basis of this result the mechanism for solidification of bubbles is discussed.