Abstract: In this study, the effects of different metal ions (NaCl, KCl, CaCl₂, AlCl₃, and FeCl₃) on the polymerization kinetics, morphology and structure of the fibril aggregates formed from whey protein isolate (WPI) were investigated. The results indicated that the final structure and characteristics of WPI fibril aggregates were affected by the different metal ions. The pH and the conductivity of the final WPI fibril aggregate solutions were increased by NaCl, KCl, and CaCl₂. While the aggregation of WPI was accelerated, the pH of the solution was reduced, and the conductivity of the solution was increased by AlCl₃ and FeCl₃. Compared with the thioflavin T (Th T) fluorescence intensity (388.92) of the native WPI fibril aggregates, the Th T fluorescence intensity increased to 465.39, 433.37, and 486.83 in response to the addition of NaCl, KCl, and CaCl₂, respectively, indicating an increase in the production of WPI fibril aggregates. In contrast, the Th T fluorescence intensity was reduced to 228.81 and 90.24 following the addition of AlCl₃ and FeCl₃, respectively, thereby indicating a reduction in the amounts of fibril aggregates generated. In addition, different metal ions altered the polymerization kinetics of WPI, reduced the (df/dt) _max value, and shortened or prolonged the period of hysteresis. The presence of AlCl₃ and FeCl₃ was found to be conducive to the clustering of WPI fibril aggregates, which became coarser and more disordered. Moreover, the Fourier transform infrared spectroscopy results indicated that NaCl, KCl, and CaCl₂ promoted the formation of β-sheet structures, whereas AlCl₃ and FeCl₃ inhibited the formation of these structures, and it was also found that addition of different metal ions altered the characteristic distances between β-chains within the fibril aggregates. These findings will provide a scientific basis for the preparation of fibril aggregates characterized by different aggregation forms using WPI.