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Two-dimensional (2D) Ruddlesden-Popper hybrid organic-inorganic perovskites are the most promising candidates for highly efficient optoelectronic devices due to their remarkable exciton characteristics, adjustable band structure and long-term environmental stability. However, excitons emission behavior of 2D Ruddlesden-Popper perovskites is still unclear. Here we theoretically-experimentally decoupled the excitons behavior in 2D Ruddlesden-Popper PEA 2 PbI 4 nanosheets. Theoretically, the Elliott theory was used to separate exciton and band edge absorptions of PEA 2 PbI 4 nanosheets and determine an exciton binding energy of about 274 meV. Experimentally, spectral-dependent photoluminescence lifetime and excitation powder density-dependent photoluminescence spectra revealed that a distinct photoluminescence tail emission should be derived from localized excitons with lower emission energy than free excitons. Further, the luminescent component of the free excitons and localized excitons with their corresponding densities of states was theoretically decoupled by line-shape analysis of PEA 2 PbI 4 nanosheets photoluminescence spectra, which is consistent with the experimental results demonstrating the existence of localized excitons. Hence, our work provides understanding on the exciton behavior and luminescence mechanism of 2D Ruddlesden-Popper perovskites, which would benefit the prediction of high-performance excitonic devices based on 2D Ruddlesden-Popper perovskites. • Excitons behavior in 2D Ruddlesden-Popper PEA 2 PbI 4 nanosheets was decoupled. • A band tail state emission derived from localized excitons. • The luminescent component of the free excitons and localized excitons was separated. [ABSTRACT FROM AUTHOR]