Abstract: To investigate the influence of varying transglutaminase (TG) levels on the fibrous structure and quality of soy texturized protein, soy protein isolate was used as the main raw material, supplemented with 0% (control), 0.1%, and 0.3% TG. High-moisture extrusion was performed using a twin-screw extruder, followed by structural characterization of the resulting texturized proteins via texture analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. Quality parameters such as color, expansion ratio, water-holding capacity, and oil-holding capacity were also evaluated. Compared with the control, TG-treated samples exhibited significantly (P<0.05) higher elasticity (0.92) and chewiness (2525.39 g), with the 0.3% TG group reaching the greatest hardness (3514.50 g). Increasing TG content significantly (P<0.05) enhanced the expansion ratio and darkened the color. Adding the appropriate amount of TG enzyme increased the water-holding capacity (by 0.1%) and oil-holding capacity (by 0.3%) of soybean histones. Scanning electron microscopy confirmed a more meat-like fibrous structure at 0.3% TG, and infrared spectroscopy revealed a shift from α-helices and β-turns toward β-sheet conformations, indicating bond breakage among protein molecules, unfolding of the native conformation, and subsequent denaturation and aggregation. This research provides a theoretical foundation for understanding texturized protein formation mechanisms and developing plant-based protein products.