Abstract: The study investigated the effects of modifying pineapple insoluble dietary fiber (PIDF) using ultrasonic (US), ultra-high-pressure homogenization (UHPH), hydrochloric acid (HCI), or alkaline hydrogen peroxide (AHP) treatment on its structural and functional properties. The correlation between PIDF structural characteristics and functional properties were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size analysis, hydration property analysis, and measurements of glucose and nitrite adsorption capacities. All four modification methods significantly altered PIDF structural characteristics and functional properties. SEM revealed increased surface folds and porosity in the modified samples, and particle size analysis demonstrated significant reductions in particle size (P<0.05). Fourier-transform infrared (FT-IR) spectroscopy revealed that no new functional groups were introduced. Among the four modification methods evaluated, alkaline hydrogen peroxide (AHP) treatment exhibited the greatest improvement in hydration properties, increasing water holding capacity to 23.91 g/g and oil holding capacity to 19.68 g/g, while ultrasonic (US) treatment yielded the highest water swelling capacity (12.78 mL/g). Regarding adsorption properties, US treatment showed the strongest glucose adsorption capacity (862.74 mg/g). AHP treatment achieved the best nitrite ion adsorption capacity at pH 2.0 (450.66 μg/g), and ultra-high pressure homogenization (UHPH) treatment was most effective for cholesterol adsorption (4.11 mg/g). These results suggest that AHP is more suitable for enhancing hydration-related properties, whereas UHPH is preferable for improving adsorption performance. In summary, the four modification methods not only altered the physical structure of pineapple insoluble dietary fiber (PIDF) but also improved its chemical functional characteristics, thereby expanding its potential applications.