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Single‐crystal halide perovskites are among the most promising semiconductor candidates for highly efficient optoelectronic devices due to their higher stability against moisture and light radiation and lower trap density than their polycrystalline counterparts. In this work, single‐crystal MAPbBr3 microcavities with controllable geometries and sizes are fabricated using a template‐limited method combined with an anti‐solvent diffusion growth method. The single‐crystal microcavities emit lasers around 550 nm under femtosecond laser excitation, with a lasing threshold of ≈35 µJ cm−2 and a quality factor of 1135, as well as excellent long‐term operation stability. The temporal‐spatial evolution of the lasing process in an individual microcavity is achieved by the microscopic optical Kerr‐gating technique. The temporal behaviors including pulse duration and build‐up time, emission spectra shift, and lasing mode evolution as a function of pump fluence are unveiled, and the complex relationship between the light‐induced carrier dynamics and lasing properties is clarified. Spatial heterogeneous lasing dynamics are also observed in an individual microdisk, which is attributed to the non‐uniform optical losses and carrier densities driven by structural imperfections. This study can provide a fabrication strategy for perovskite on‐chip optoelectronic devices, as well as a deeper understanding of the carrier‐density‐driven lasing dynamics in microcavities. [ABSTRACT FROM AUTHOR]