High‑mobility‑group‑box chromosomal protein 1 (HMGB1) is a ubiquitous and abundant nuclear protein in eukaryotic cells. Nuclear HMGB1 serves an important role in maintaining nuclear stability under stress. However, extracellular HMGB1 exerts actions, which are distinctly different compared with these intracellular functions. HMGB1, when released extracellularly, is a potent innate signal, which initiates host defense mechanisms or tissue regeneration. HMGB1 has two DNA‑binding domains: HMG A box and B box. The HMGB1 A box exhibits an antagonistic, anti‑inflammatory effect, and is a potential therapeutic target, however, the large‑scale expression and purification of the HMGB1 A box with high efficiency remains to be reported. In the present study, a SUMO‑fusion expression system was used to express and purify high levels of functional HMGB1 A box to meet the requirements of therapeutic protein production.