approach to realize new functionalities through facile van der Waals coupled 2D layers. [6] Owing to the large dielectric mismatch between the inorganic and organic layers, the quasi-2D RPPs naturally form quantum well structures, in which, the inorganic and organic layers serve as potential wells and barriers, respectively. [7] Moreover, these quantum confined structures impart the appealing characteristics of improved environmental stability and enhanced exciton confinement. [2] These make the quasi-2D RPPs promising for solar cell and light-emitting diode (LED) applications. [5,[8][9][10] Recently, the amplified spontaneous emission (ASE) and lasing behaviors of 2D RPPs have been demonstrated. [11][12][13][14][15][16][17] However, the lasing is mostly obtained from solution-processed spin-coated thin films, in which multiple RPP components inevitably form with different bandgaps that drive cascade carrier transfer and may reshape the build-up of population inversion. [11,14,15,18] Also, the development of continuous-wave or electrically driven RPP lasers central for practical applications is still challenging. The exploitation of homologous RPP lasers is of great importance to gain further insights into the intrinsic lasing mechanisms of these quantum well-like structures as well as the design of low-threshold 2D 2D Ruddlesden-Popper perovskites (RPPs) have aroused growing attention in light harvesting and emission applications owing to their high environmental stability. Recently, coherent light emission of RPPs was reported, however mostly from inhomologous thin films that involve cascade intercompositional energy transfer. Lasing and fundamental understanding of intrinsic laser dynamics in homologous RPPs free from intercompositional energy transfer is still inadequate. Herein, the lasing and loss mechanisms of homologous 2D (BA) 2 (MA) n −1 Pb n I 3n+1 RPP thin flakes mechanically exfoliated from the bulk crystal are reported. Multicolor lasing is achieved from the large-n RPPs (n ≥ 3) in the spectral range of 620-680 nm but not from small-n RPPs (n ≤ 2) even down to 78 K. With decreasing n, the lasing threshold increases significantly and the characteristic temperature decreases as 49, 25, and 20 K for n = 5, 4, and 3, respectively. The n-engineered lasing behaviors are attributed to the stronger Auger recombination and exciton-phonon interaction as a result of the enhanced quantum confinement in the smaller-n perovskites. These results not only advance the fundamental understanding of loss mechanisms in both inhomologous and homologous RPP lasers but also provide insights into developing low-threshold, substrate-free, and multicolor 2D semiconductor microlasers.2D Ruddlesden-Popper perovskites (RPPs), with the general chemical formula of L 2 (MA) n−1 M n X 3n+1 , are composed of welldefined inorganic layers with corner connected [MX 6 ] 4− octahedra and long organic chains (L + ) intercalated between these inorganic fragments. [1][2][3][4][5] This structure promises a viable