A novel fluorescence turn-on method for sensitive and selective detection of protamine was developed based on aggregation-induced emission enhancement (AIEE) characteristics of 4-(6'-carboxyl)hexyloxysalicylaldehyde azine (CHSA) induced by electrostatic interaction between protamine and CHSA(-). Under optimal conditions described, a large Stokes shift of approximately 198 nm could be observed, and the fluorescence enhancement at 538 nm was linearly related to the concentration of protamine in the range of 0.6-18 microg mL(-1) with the relative correlation coefficient of R(2) = 0.9996 (n = 11) and a detection limit as low as 43 ng mL(-1). The relative standard deviation (R.S.D.) was 2.0% (n = 5). The proposed method was successfully utilized in quantifying protamine in diluted horse serum. In addition, due to the special electrostatic association between protamine and heparin, CHSA could also be employed as a probe to study the interaction between them.