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Metal halide perovskite light‐emitting diodes (PeLEDs) are promising high‐definition display candidates due to their narrow emission bandwidth and wide color gamut. However, efficient and stable pure‐red PeLEDs have rarely been achieved. Herein, a robust and strongly‐coordinated sulfate anion passivation strategy is reported to achieve a spectrally stable and efficient pure‐red PeLED with an electroluminescent peak at 630 nm and full width at half maximum of 27 nm. Octylammonium sulfate is employed to construct a PbSO4 layer on the surface of CsPbI3−xBrx nanocrystals, which can effectively inhibit phase separation under UV light, humidity, or heat treatment. Using sulfate passivated CsPbI3−xBrx NC film, pure red PeLEDs with high external quantum efficiency of 12.6%, excellent spectral stability, and an operational half‐life time of over 300 min (T50@100 cd cm−2) are fabricated. This work provides a new avenue to improve performance of pure red PeLEDs via strong‐coordinated sulfate passivation. [ABSTRACT FROM AUTHOR]