Ceramic samples with the nominal composition (1-x) BaTiO3 +x Ba3Ti2YO8.5 (x=0-0.535) were prepared by the mixed oxide method. X-ray diffraction (XRD) analysis shows that the materials are of single phase with a cubic symmetry as x <= 0.16. The compositions of the solid solutions (x <= 0.16) can be expressed equivalently as Ba(Ti1-yYy)O3-delta (y <= 0.122, y=x/(1+2x)). For x > 0.16, the materials are diphasic composites consisting of Ba(Ti1-yYy)O-3 (y=0.122) and Ba3Ti2YO8.5. The microstructure observation by scanning electron microscopy supports the XRD result. The dielectric behavior and phase transitions of the solid solutions (x <= 0.16) vary with different Y concentrations. The dielectric constant of the composites (x > 0.16) follows approximately the Lichteneker relation in a wide temperature range.