Abstract: Objective:To study the effect of Nostoc sphaeroides on laxative in constipation rats and explore the related mechanisms of relieving constipation. Methods:Rats were randomly divided into control group,model group and Nostoc sphaeroides group. The model group and the Nostoc sphaeroides group were intragastrically administered with Nostoc sphaeroides for 3 weeks and then administered with loperamide hydrochloride for 1 week. The rats in the control group were given the same amount of normal saline. The first black sputum time was observed by intragastric administration of the ink. Hematoxylin-eosin(hematoxylin-eosin,HE)staining and alixin blue-periodic acid Schiff(AB-PAS)staining were used to observe colonic structure and mucus secretion. Results:Compared with the model group rats,Nostoc sphaeroides group's intervention with Nostoc sphaeroides extremely significantly increased the fecal weight and water content of constipated rats(P<0.01),and extremely significantly shortened the first black stool generation time(P<0.01). The structure of the colonic muscular and mucosal layers was improved,the number of goblet cells and the content of mucus increased significantly(P<0.05). Conclusion:Nostoc sphaeroides could significantly improve the intestinal water content,strengthen intestinal peristalsis,increase mucus secretion,protect intestinal tissues,and effectively improve constipation symptoms.