Halide perovskite nanocrystals (PeNCs) have emerged as a class of excellent semiconductors in the past few years for their high-performance optoelectronic applications. These materials have received considerable attention due to efficient charge carrier mobility, high photoluminescence quantum yields (PLQYs) and near theoretical efficiencies for green emitters. However, methylammonium (MA) cation-based perovskites exhibit their inherent instability such as high sensitivity to light, heat, oxygen, and moisture which influence their performance in practical applications. Their low in production cost and ease of synthesis make them suitable candidate for upcoming technologies. In this research, we study the doping of Cs and Rb cations into MAPbBr3 PeNCs to optimize their morphology, crystal structure, and optical properties. It is found that rubidium cations doping can greatly enhance the photoluminescence intensity of the MAPBBr3 PeNCs, whereas cesium cations can improve the structural stability owing to the increased valance bond intensity. This work provides useful thoughts for the synthesis of high-performance optoelectronic devices based on mixed-cation PeNCs.