Abstract: In recent years, with the development of 5G mobile communication, the development of communication technology has attracted more and more attentions. As the most widely used material in communication field, microwave dielectric ceramics have also raised higher requirements for their dielectric properties, including appropriate dielectric constant (ε_r), as high as possible Q×f value, and close to zero frequency temperature coefficient (τ_f). For a perovskite-structured material, using an appropriate doping to increase its Q×f value is an effective method. In this work, the microwave dielectric ceramics of SrTi_(1-1.25x)Nb_xO₃ doped with stoichiometric Nb₂O₅ were prepared by a conventional solid-state route. The phase composition, microstructures and microwave dielectric properties of the ceramics (x:0-0.005) were investigated. The results show that when x increases from 0 to 0.005, both the phase composition and volume density of SrTi_(1-1.25x)Nb_xO₃ keep stable without obvious changes. On the other hand, with the increasing of Nb⁵⁺ ion content, the number of small grains in the crystal keeps decreasing while the size of the large grain increases rapidly. Meanwhile, the dielectric constant (ε_r) is unchanged basically, while the Q×f value is increasing. When x is 0.005, the excellent microwave dielectric properties, i.e., 296.41 of ε_r, 6 953 GHz of Q×f could be obtained for the ceramics of SrTi_(1-1.25x)Nb_xO₃ (SrTi_{0.993 75}Nb_0.005O₃) dielectric.