The industrial processing of Aconitum carmichaelii roots for use in Traditional Chinese Medicine generates a high amount of waste material, especially leaves. An acidic polysaccharide fraction isolated from these unutilized leaves, AL-I, was in our previous work shown to contain pectic polysaccharides. This study aimed to investigate the protective effect of AL-I on ulcerative colitis for the possible application of A. carmichaelii leaves in the treatment of intestinal inflammatory diseases. AL-I was found to alleviate symptoms and colonic pathological injury in colitis mice, and ameliorate the levels of inflammatory indices in serum and colon. The production of short- and branched-chain fatty acids was also restored by AL-I. The observed protective effect could be due to the inhibition of NOD1 and TLR4 activation, the promotion of gene transcription of tight-junction proteins, and the modulation of gut microbiota composition like Bacteroides , Dubosiella , Alistipes and Prevotella ,. A regulation of serum metabolomic profiles being relevant to the bacterial change, such as _D -mannose 6-phosphate, _D -erythrose 4-phosphate and uric acid, was also observed.