Intestinal mucosal barrier loss is responsible for the chronic and recurrent ulcerative colitis. Myosin light chain kinase (MLCK) is a potential therapeutic target of the intestinal mucosal barrier dysfunction. Here, we developed a reactive oxygen species (ROS)-sensitive hydrogel (ATG-CS-Gel) derived from a diselenide-bridged arctigenin (ATG) and chitosan (CS) conjugate, with the aims of targeting to inflamed mucosa and modulating MLCK. Our results demonstrated that ATG-CS-Gel achieved ROS-responsive release and significantly inhibited ROS production and mitochondrial depolarization in the Caco-2 and HT-29/MTX-E12 cells under HO-induced stress conditions. Compared with normal tissues, orally-administrated ATG-CS-Gel preferentially adhered to the inflamed mucosa for 24 h, which was attributed to the adhesion between CS and mucin. Therapeutically, ATG-CS-Gel reduced inflammatory symptoms, accelerated intestinal mucosal healing, scavenged excessive ROS, reshaped intestinal flora, and eventually achieved much better therapeutic efficacy in DSS-induced colitis mice when compared to 5-aminosalicylic acid. Moreover, ATG-CS-Gel was demonstrated to reverse intestinal mucosal barrier loss by blocking MLCK activation and maintaining tight junction expression. In summary, this study highlights the potential of MLCK modulation in the restoration of intestinal mucosal barrier using ATG-CS-Gel. The development of ATG-CS-Gel represents a novel and promising strategy for the treatment of ulcerative colitis.