Abstract In hybrid organic–inorganic and all-inorganic metal halide perovskite nanomaterials, two-dimensional (2D) Ruddlesden–Popper (RP) perovskites have become one of the most interesting materials because of tunable bandgaps varied with the layer thickness, effective modulation of the electron-hole confinement, and high stability. Here, we report a one-pot synthesis of 2D RP perovskite (BA)2(MA)n − 1PbnX3n + 1 (BA = 1-butylammonium, MA = methylammonium, X = Br or I) quantum dots (QDs) with an average size of 10 nm at room temperature. The (BA)2(MA)n − 1PbnBr3n + 1 (Br series) QDs and (BA)2(MA)n − 1PbnI3n + 1 (I series) QDs exhibited tunable emitting spectrum in the range of 410–523 nm and 527–761 nm, respectively, with full width at half maximum (FWHM) of 12–75 nm. The emission color was tuned by the ratio of MA and halide. The photoluminescence quantum yield of 2D perovskite QDs reached 48.6% with more thermodynamic stability in comparison with 3D MAPbX3 QDs. Overall results indicated that developing a solution synthesis for 2D RP perovskite QDs with great optical properties paves the way toward future optoelectronic devices and perovskite quantum dot photovoltaics.