Lead halide perovskite microlasers have shown impressive performance in the green and red wavebands. However, there has been limited progress in achieving blue-emitting perovskite microlasers. Here, blue-emitting perovskite-phase rubidium lead bromide (RbPbBr3) microcubes were successfully prepared by using a one-step chemical vapor deposition process, which can be utilized to construct optically pumped whispering gallery mode microlasers. By regulating the growth temperature, we found that a high-temperature environment can facilitate the formation of the perovskite phase and microcubic morphology of RbPbBr3. Notably, blue single-mode lasing in a RbPbBr3 microcubic cavity with a narrow linewidth of 0.21 nm and a high-quality factor (∼2200) was achieved. The obtained lasing from RbPbBr3 microlasers also exhibited an excellent polarization state factor (∼0.77). By modulating the mixed-monovalent cation composition, the wavelength of the microlaser could be tuned from green (536 nm) to pure blue (468 nm). Additionally, the heat stability of the mix-cation perovskite was better than that of conventional CsPbBr3. The stable and high-performance blue single-mode microlasers may thus facilitate the application of perovskite lasers in blue laser fields.