Strontium barium niobate/strontium barium titanate (SBT) composite ceramics with different Nb/Ti ratios, [y(Sr0.3, Ba0.7)Nb2O6/(1 − y)(Sr0.3, Ba0.7)TiO3], were fabricated using a Powder–Sol (P–S) method by suspending Nb2O5 powders in the sol solution of SBT. The microstructure of composite ceramics was characterized by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. Homogeneous and fine-grained composite ceramics were successfully prepared by P–S method. Tetragonal tungsten bronze phase and perovskite phase were revealed co-present in the composite ceramics, whose phase structure was dependent on the pre-sintering temperature and Nb/Ti ratios. The substitution reactions were proposed to explain the formation mechanism of the composite ceramics.