nanolasers generating laser emission in the range of 420-824 nm, [1][2][3][4] , which can be simply synthesized from solution. First of all, such perovskites possess relatively high refractive index (larger than 2), which allows for the creation of self-resonating gain media placed on various substrates: dielectrics, [1][2][3][4] metals, [5] nanostructured, [6] photonic crystals, [7] as well as integrated with waveguiding systems. [8][9][10] Also, chemically synthesized CsPbX 3 perovskite single crystals [11] of high quality and different shapes (cuboids, [12,13] wires, [1,14,15] plates [16][17][18] ) exhibit high levels of optical gain (typically ≈10 3 cm −1 ) [19] larger than those of thin polycrystalline films synthesized from solution (typically ≈10 2 cm −1 ). Thus, they provide a powerful technological tool for micro-and nanolasers fabrication, when their precise positioning is not required. However, the fabrication of large-scale films with crystalline quality as high as for single crystals would allow for overcoming many technological obstacles hindering lithographical creation [9,20,21] of highly controllable designs for lasing applications.In this paper, we develop a high-temperature recrystallization method for chemical synthesis of large-grain CsPbBr 3 thin Halide perovskite lasers based on CsPbBr 3 micro-and nanoscale crystals have demonstrated fascinating performance owing to their low-threshold lasing at room temperature and cost-effective fabrication. However, chemically synthesized thin films of CsPbBr 3 usually have rough polycrystalline morphology along with a large amount of crystal lattice defects and, thus, are mostly utilized for the engineering of light-emitting devices. This obstacle prevents their usage in many photonic applications. Here, a protocol to deposit large-grain and smooth CsPbBr 3 thin films is developed. Their high quality and large scale allow to demonstrate a maximum optical gain up to 12 900 cm −1 in the spectral range of 530-540 nm, which is a record-high value among all previously reported halide perovskites and bulk semiconductors (e.g., GaAs, GaN, etc.) at room temperature. Moreover, femtosecond laser ablation technique is employed to create high-quality microdisc lasers on glass from these films to obtain excellent lasing characteristics. The revealed critical roles of thickness and grain size for the CsPbBr 3 films with extremely high optical gain pave the way for development of low-threshold lasers or ultimately small nanolasers, as well as to apply them for polaritonic logical elements and integrated photonic chips.