The appropriate composite ratio of cationic polymer and gene is fundamental but paramount determinant for efficient gene condensation. In this study, we proposed to construct a novel strategy to comprehensively understand gene condensation situation by using the pyrene (Py) modified polyethylenimine as fluorescent self-reporter, owing to the unique monomer and excimer fluorescence of Py groups highly depending on their intermolecular interval. Constant with the traditional measurements for polymer-gene complex including gel retardation analysis, DLS, zeta -potential, and TEM, the typical curve of fluorescence intensity ratio at I-380/I-490 was verified to easily have an insight into the gene condensing process, and further recommend the appropriate range of NIP ratio (the ratios of moles of the amine groups of cationic polymers to those of the phosphate ones of DNA) for enhancing gene delivery. Thus, the facilely fabricated fluorescigenic cationic polymer based on an unique excimer-monomer switch could be used as an novel fluorescent self-reporter for comprehensively discerning the gene condensation, which may provide a feasible way to improving the optimal gene encapsulation for efficient and safe gene delivery. (C) 2018 Elsevier B.V. All rights reserved.