The La(Cr1‐xMnx)O3(x = 0 to 0.25) system exhibited a displacive phase transformation from an orthorhombic to a rhombohedral structure at temperatures ranging from about 256°C atx= 0 to 305°C atx= 0.25. The Rietveld method of X‐ray analysis was used to determine structural characteristics and to assay phase concentrations when multiple phases were present. Indications were that the Mn ions on the B site affected the transition temperature through an ionic size effect; i.e., Mn3+, with a larger ionic size than Cr3+, increased the transition temperature while the presence of the smaller Mn4+ions reduced it. A hysteresis was also observed with respect to the phase transformation as a function of temperature. The phase transformation was associated with a change in the rotation of the oxygen octahedra from an antiphase to an in‐phase tilt s