Abstract The Mn-based perovskite oxides are of strong current interest because they show a colossal negative magnetoresistance near the ferromagnetic ordering temperature. The samples become metallic below T c for a content of approx. 30% Mn 4+. We present in this article a structural study of La 1− x Sr x MnO 3 for compositions lying below the optimum magnetoresistance. At high temperature, the system is rhombohedral ( R 3 c). On cooling, two stuctural transitions to orthorhombic Pbnm phases (O and O′) take place successively. The transition from the O to the O′-phase is due to the setting up of co-operative Jahn-Teller distortions that become state in the O′-phase. The O′-phase is characterised by the presence of an anti-ferrodistorsive Mn 3+ orbital ordering. This ordering is evidenced by a peculiar arrangement of distorted MnO 6 octahedra: the connection between octahedra in the basal lane ( a, b) shows long MnO bonds adjacent to short MnO bonds. The peculiarity of samples around the composition x = 0.125 is that they undergo another transition to an orthorhombic O″-phase at lower temperatures. This phase has the same average structural features as the O-phase but the Jahn-Teller distortion seems to be completely suppressed.