Herein, we demonstrate a simple approach for tuning the elecrochemiluminescence (ECL) properties of CsPbBr₃ perovskite nanocrystals (NCs) by using mixed-monovalent cations. By replacing some of the Cs⁺ with Rb⁺, a series of Rb_xCs_1−xPbBr₃ NCs were obtained. They exhibit a narrow ECL emission peak with a full width at half-maximum of about 26–34 nm. After continuously injecting holes to produce different charged state radicals, an annihilation ECL was observed, implying that the as-prepared Rb_xCs_1−xPbBr₃ NCs are in an electron-rich state. In the presence of 2-dibutyaminoethanol as a co-reactant, strong anodic ECL of Rb_xCs_1−xPbBr₃ NCs was obtained. From CsPbBr₃ NCs to RbPbBr₃ NCs, the ECL peak potential position moved from 1.25 V to 1.80 V with the ECL spectrum peak shifting from 512 to 468 nm, respectively, indicating the tunable ECL properties. The Rb_0.2Cs_0.8PbBr₃ NCs have a higher ECL intensity than the CsPbBr₃ NCs.