Polycrystalline samples of perovskite (Ba,Rb)BiO3 have successfully been synthesized in a short time of 2 h at a temperature as low as 310°C by the direct precipitation from molten RbOH. The powder x-ray diffraction pattern has revealed the formation of well-crystallized Ba 1-xRbxBiO3 with 0.31<x<0.40. The appearance of superconductivity has been confirmed by the magnetic susceptibility measurements for all samples. The superconducting transition temperature Tc has a maximum value of ∼28 K at x∼0.37, which is quite similar to that of (Ba,K)BiO3. These results are in good agreement with those of samples obtained by the conventional solid-state reaction method.