The phase assemblage, crystal structure evolution and microwave dielectric response of (Ca0.5+xSr0.5-x) [(Al0.5Nb0.5)(0.5)Ti-0.5]O-3 ceramics (abbreviated as CSANT hereafter) are investigated. Single perovskite solid solution is formed in the CSANT ceramics in Sr-rich composition range of x < -0.05, however, Ca4Ti3O10-type layered perovskite phase begins to segregate after x = -0.05. The CSANT perovskites crystallized in Fm3m cubic symmetry in the composition range of x <= 0.2, however, as the Ca2+ content in A-site increased, the oxygen octahedral began to be anti-phase tilted at x = -0.1 and the crystal structure transited to P2(1)/n pseudo-orthorhombic space group thereafter. The microwave dielectric response of the CSANT ceramics is elaborately discussed in terms of their crystallographic structure and chemical composition. When sintered at 1500 degrees C for 4 h, a dielectric constant epsilon(r) of 52.5, a Qf product of 28000 GHz and a tau(f) of +25.4 ppm/degrees C microwave dielectric ceramic can be obtained in the CSANT ceramics at x = 0.3. (C) 2013 Elsevier B. V. All rights reserved.