Samples with nominal compositions La_1.2 (Sr_1-x Ca_x )_1.8 Mn₂ O₇ (x = 0.00, 0.25, 0.50, 0.65, 0.80 and 1.00) have been prepared and characterized by x-ray diffraction (XRD) and ac susceptibility techniques. Drastic changes in the XRD pattern and in the ac susceptibility versus temperature behaviour at x = 0.65 indicate that single phase compounds with layered Sr₃ Ti₂ O₇ structure are formed only up to x = 0.50. Rietveld refinement of the XRD patterns of x = 1.00 composition suggests that the compositions with x 0.65 form multiphase mixtures comprising hole doped perovskite manganates as majority phases and CaO as the minority phase. These results are at variance with the literature reports that the compound La_1.2 Ca_1.8 Mn₂ O₇ forms with layered Sr₃ Ti₂ O₇ structure.