The polycrystalline sample of Ba2Co1.5Mg0.5Fe11.88Ga0.12O22 Y-type hexaferrite, doped with Ga-cation, was prepared by using the solid-state reaction method. The crystalline structure of sample was investigated by x-ray diffractometer (XRD), and the magnetic properties of sample were measured by vibrating sample magnetometer (VSM), and Mössbauer spectrometer. The crystal structure of prepared sample was determined to be rhombohedral with space group R-3m. From the temperature dependence of the magnetization curves under 100 Oe between 4.2 and 740 K, two temperature-dependent magnetic transitions occurred in the Ba2Co1.5Mg0.5Fe11.88Ga0.12O22 sample. Mössbauer spectra of the sample were analyzed at various temperatures ranging from 4.2 to 620 K, and the Ba2Co1.5Mg0.5Fe11.88Ga0.12O22 sample showed abrupt changes in Hhf and EQ at 200 K, indicating the spin transition effect. We have also determined the magnetic transition temperature TC, in addition to the temperature dependent magnetization and ZVC measurements.