The series of complex aluminates RE₂SrAl₂O₇ (RE = La, Nd, Sm, Eu, Gd, Tb, Dy, Ho) was prepared at 1450°C. Their structure is the double perovskite slab-rocksalt layer P₂/RS intergrowth of the n = 2 Ruddelsden-Popper phases. X-ray Rietveld refinement calculations point to a progressive RE-Sr ordering between the ninefold sites in the RS layers and the twelvefold one in the P₂ slabs, respectively. This ordering proves both to improve the ease to prepare these aluminates and stabilize their intergrowth structure. The limit observed for RE = Ho corresponds to a nearly fully ordered distribution of the Ho³⁺ and Sr²⁺ cations - 91%. Due to an excess structure-bonding anisotropy in the ninefold sites, a further extent to smaller RE³⁺ cations is unsuccessful. These results well compare with those regarding the magnetoresistant manganites RE₁ + _xSr₂ - _xMn₂O₇: increasing RE-Sr ordering and limit found for Er. The big size A element long range ordering phenomena which are unlikely to depend on redox phenomena of the B element in the P₂ slabs, have to be considered as specific trends of the P₂/RS intergrowth type complex oxides.