Formamidinium (CH(NH₂)₂, FA) lead halide perovskites exhibit excellent optoelectronic properties for the applications of light-emitting diodes and lasers. However, the reported formamidinium lead bromide (FAPbBr₃) perovskite-based lasers mainly depend on the external feedback or Fabry–Pérot mode cavities and suffer from moderate quality (Q) factors. Herein, solution-processed square and quasi-circular FAPbBr₃ microdisks are developed to achieve room-temperature naturally facet-formed whispering gallery mode (WGM) lasers. These microdisks exhibit relatively high Q factor and tunable laser modes with threshold of 10–70 µJ cm⁻² under 400 nm excitation. Although the synthesized circular microdisk is not regular enough, it still shows higher Q factor of 3455 than that of square microdisk due to the less boundary wave and pesudointegrable leakage. This simple and low-cost solution processed method can tackle the complicated and expensive conventional preparation techniques of circular microdisks. Power dependent photoluminescence decay transients indicate that the band edge emission of the FAPbBr₃ microdisks originates from free carrier recombination. In addition, these microdisks show high photostability and that room temperature lasing can sustain over 50 min. These results suggest that FAPbBr₃ microdisks can serve as promising WGM lasers with excellent light emission capability and stability toward practical optoelectronic applications.