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Exciton localization is an approach for preparing highly luminescent semiconductors. However, realizing strongly localized excitonic recombination in low‐dimensional materials such as two‐dimensional (2D) perovskites remains challenging. Herein, we first propose a simple and efficient Sn2+ vacancy (VSn) tuning strategy to enhance excitonic localization in 2D (OA)2SnI4 (OA=octylammonium) perovskite nanosheets (PNSs), increasing their photoluminescence quantum yield (PLQY) to ≈64 %, which is among the highest values reported for tin iodide perovskites. Combining experimental with first‐principles calculation results, we confirm that the significantly increased PLQY of (OA)2SnI4 PNSs is primarily due to self‐trapped excitons with highly localized energy states induced by VSn. Moreover, this universal strategy can be applied for improving other 2D Sn‐based perovskites, thereby paving a new way to fabricate diverse 2D lead‐free perovskites with desirable PL properties. [ABSTRACT FROM AUTHOR]