Ba4(Ce0.5Sm0.5)9.3Ti18−z Al z O54 (BCSTA, z = 0, 0.25, 0.50, 0.75, 1.00) ceramics sintered in nitrogen atmosphere were prepared by the conventional solid state reaction. The effects of Al3+ substitution for Ti4+ on microstructure and microwave dielectric properties in BCSTA ceramics have been investigated. X-ray diffraction spectra revealed only a single tungsten bronze in all the samples from z = 0 to z = 1.00 and backscatter electronic images confirmed a second BaAl2Ti5O14 phase at z > 0.50. Besides, XPS results indicated that the incorporation of Al3+ suppressed the reduction of Ti4+, which leaded to the microwave dielectric properties such as Q × f and τ f value improvement in BCSTA ceramics. Typically, the optimum combination of microwave dielectric properties: Q × f ∼ 8401.76 GHz, e r ∼ 71.68, and τ f ∼ +4.37 ppm/°C were obtained at z = 0.50 in BCSTA ceramics sintered in nitrogen atmosphere.