To investigate the crystallographic deformation characteristic of pure Al under static and cyclic stress at 0.4Tm, the compressive creep tests were performed on single crystal of 99.99% aluminum rod, Irrespective of crystallographic orientation, mostly one slip system is operated at the steady state under the condition of cyclic creep acceleration and the spacing of slip steps of the operating slip system is observed to be narrower in the cyclically crept specimen than that of statically crept one. This result implies that the cyclic creep acceleration is due to the enhanced dislocation climb by the cyclic stressing. The lower value of the activation energy of cyclic creep than that of static creep also supports those results.