In this work, we prepare Ba 1−x Sr x Ti 0.9 Mn .01 O 3-δ (x = 0.00, 0.01, 0.03, 0.05, and 0.07) ceramics by the mixed oxide method and study the relationship between phase transition and dielectric property of the ceramics. The phase of the samples transformed from a hexagonal phase to mixed phases due to the increase in Sr doping amount.The X-ray diffraction (XRD) profiles and Raman spectra of the samples also show the same phase transformation due to increasing Sr doping amount. The XRD pattern of the undoped sample indicates a single h-BaTiO 3 phase with P6 3 /mmc symmetric space group, while the samples with high Sr doping amounts have a mixed phase with t-BaTiO 3 with P 4 mm symmetric space group. The scanning electron microscopy images show two types of BaTiO 3 grains, which grew with increasing sintering temperature. With increasing Sr concentration, the K-values (relative dielectric constant) of the ceramics increased, while the Q xf values (the quality factor multiplied by frequency) decreased, which indicate that the microwave dielectric property is related to phase transformation. K E Y W O R D Sdielectric property, hexagonal BaTiO 3 , phase transformation, Sr-doping