Abstract: This study investigated the changes in major chemical components, physical properties, and physiological activities of Polygonatum sibiricum during nine-steam-nine-bake (a traditional Chinese medicine processing technique). First, the colorimetric method, texture analyzer, colorimeter, and moisture analyzer were utilized to quantify the contents of major components and characterize the variations in physical properties of Polygonatum sibiricum throughout the processing. Two analytical approaches were applied to elucidate the overall variation trends. Second, the antioxidant capacity, α-glucosidase inhibitory rate, and effects on macrophage viability and phagocytic capacity of Polygonatum sibiricum at different processing stages were determined to comprehensively evaluate the alterations in functional activities during the steaming and baking process.The results demonstrated that the total sugar content decreased to 32.48 mg/g during processing, while the contents of polyphenols, flavonoids, anthraquinones, and melanoidins increased to 10.28, 14.68, 10.90, and 17.39 times those of the raw sample, respectively. The color parameter E*ab declined from 62.21 to 40.34, corresponding to a color transition from yellowish-white to dark brown. The texture became softer without structural disruption. Overall, the nine-steam-nine-bake process could be divided into three stages: Initial stage (raw P. sibiricum and one cycle of steaming and baking), middle stage (two to four cycles of steaming and baking), and final stage (five to nine cycles of steaming and baking). The contents of total sugar, total phenols, flavonoids, anthraquinone compounds, and melanoidins in Polygonatum sibiricum were significantly correlated with its color, thus the contents of these components could be predicted by color indicators. At a concentration of 3.0 mg/mL, the extract of Polygonatum sibiricum processed by nine-steam-nine-bake exhibited scavenging rates of 80.22% and 96.67% for DPPH and ABTS⁺ free radicals, respectively. At 10 mg/mL, it showed an α-glucosidase inhibitory rate of 63.29%. Within the concentration range of 50~400 μg/mL, the extract was non-cytotoxic toward macrophages, while also promoting macrophage proliferation and enhancing phagocytic capacity, thereby demonstrating the strongest physiological activity. In conclusion, the changes in major component contents, physical properties, and physiological activities of Polygonatum sibiricum during nine-steam-nine-bake follow distinct regularity. This study provides a scientific reference for deciphering the mechanism of the nine-steam-nine-bake technique and developing quality assessment criteria for processed Polygonatum sibiricum.