AbstractGreat progress has been made in high‐performance perovskite light‐emitting diodes (PeLEDs). However, the external quantum efficiency (EQE) of blue PeLEDs still lags. Particularly, defects are inevitable in solution‐processed perovskite films, which inhibit the efficient radiative recombination in blue PeLEDs. Herein, a facile ionic liquid (IL, 1,3‐dimethyl‐3‐imidazolium hexafluorophosphate) post‐treatment on the as‐fabricated quasi‐2D perovskite film is reported, to passivate the uncoordinated Pb through the strong interaction with IL. The IL‐assisted perovskite film demonstrates a great enhancement of radiative recombination efficiency, and the photoluminescence quantum yield of the film increases from 35.7% to 74.6%. IL post‐treatment also adjusts the energy level of perovskite film and enhances the hole injection in PeLED. As a result, the peak EQE of the sky‐blue quasi‐2D PeLED is improved from 4.0% to 9.0%, while the turn‐on voltage is reduced from 3.3 to 3.0 V. This work contributes to a feasible and effective approach for improving the quality of blue quasi‐2D perovskites and enhancing the efficiency of blue PeLEDs.