Ceramic samples of the melilite-type La1+xSr1-xGa3O7-delta (x = -0.15 to 0.60) compound were prepared by conventional ceramic processing. Sintering characteristics and microstructural evolution were studied. A phase diagram study was performed to establish the solid solubility limits as a function of the La:Sr ratio. Structural investigations of the Dalton composition as well as strontium- and lanthanum-rich samples entailed X-ray, neutron, and electron diffraction techniques at ambient and elevated temperatures. The homogeneity region was remarkably broad (x = -0.15 to 0.60) with no changes in space group observed. A small shrinkage of the unit cell was found with increased lanthanum content. Phase transitions at ambient and intermediate temperatures did not occur.