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The syntheses of LiOsO₃ and NaOsO₃ have brought some fresh input to the long-standing dialogs of ferroelectric metal and the metal-insulator transition. The LiOsO₃ with the LiNbO₃-type structure has been believed to be the best candidate for the ferroelectric metal proposed by Anderson and Blount [1]. Whether the metal-insulator transition in the orthorhombic perovskite NaOsO₃ [2] can be attributed to either a Mott transition or a Slater transition is still controversial [3,4].  KOsO₃ in this family has been synthesized under a high-pressure and high-temperature condition for the first time. As the geometric tolerance factor is close to 1, the perovskite KOsO₃ crystallizes in a cubic structure (Pm-3m). The cubic phase remains stable for a large range of the Na doping in K_1-xNa_xOsO₃. The perovskite KOsO₃ and the Na-doped KOsO₃ samples were characterized by the measurements of magnetic susceptibilities, thermoelectric power, and specific heat. In the talk, we will present the measurement results and the magnetic structure by neutron diffraction.