Herein, we successfully functionalized polyethyleneimine (PEI) with 3-allylrhodanine (ARD) by two-step reac-tion to get a PEI derivative (PEI-ARD) with an aggregation-induced emission enhancement (AIEE) performance as a fluorescent specific probe for Ag+ ions. For the PEI-ARD, the intramolecular aggregation of rhodanine heterocycle and its appropriate content along PEI chains play an important role in regulating their AIEE per-formance. To our surprise, PEI-ARD specifically recognized and detected Ag+ ions even in coexistence with other metal ions. The sensitivity of the specific detection of PEI-ARD to Ag+ was significantly increased by the enrichment of rhodanine moieties on PEI, and its limit of detection (LOD) was as much lower as 90.7 nM, which was rarely reported. We also fabricated the reversible detection system to Ag+ with the help of the stronger complexation of SCN- ions. In addition, the complexation constant, the complexing ratio of PEI-ARD to Ag+ and the mechanism of specific detection to Ag+ ions were systematically explored through 1H NMR titration and FT-IR techniques. In a word, PEI-ARD with AIEE is expected as an ideal functional material for the detection and recognition of Ag+ ions in environment and body fluids.