Jichuan decoction (JCD) is a well-known traditional Chinese medicinal formula that moistens the intestines and is widely used for the treatment of constipation in China. However, its effects and mechanisms in alleviating slow transit constipation (STC) in vivo remain unclear. We attempted to demonstrate the effect of JCD, with and without essential oil (VO), on intestinal transit and its underlying molecular mechanisms in rats with loperamide-induced STC.Water consumption, body weight, fecal water content, time to first melena excretion, and intestinal transit ratio of the animals were measured. 5-Hydroxytryptamine (5-HT), substance P (SP), vasoactive intestinal peptide (VIP), and interleukin-6 (IL-6) levels in the sera of rats were evaluated using ELISA. Hematoxylin and eosin and Periodic Acid-Schiff staining were used to determine intestinal tissue histology, while quantitative real-time PCR, western blotting, and immunohistochemical analysis were used to assess the relative expression levels of cAMP/PKA/AQPs pathway- and inflammation-related proteins. 16 S rDNA sequence analysis of rat feces was used to determine the diversity and abundance of the intestinal flora.The JCD groups showed reduced time to first melena excretion and expression of VIP and IL-6. The JCD groups, specifically JCD + VO groups, showed increased fecal water content, intestinal transit rate, and SP expression. Further, these groups showed improved histological characteristics of the colon, with no significant change in the index of immune organs or morphological characteristics of other organs. In addition, a significant decrease in the activation of the cAMP/PKA/AQPs signaling pathway in the colon tissue was observed in these groups, specifically the JCD + VO groups. Moreover, treatment with JCD, with or without VO, downregulated the expression of inflammatory factors and enriched the diversity of intestinal flora as evidenced by polymorphism analysis and the contents of Bacteroides, Lactobacillus, and Erysipelas, with the JCD + VO groups showing better therapeutic outcomes.JCD improved loperamide-induced STC, and co-administration with VO exhibited better activity than sole JCD therapy. JCD may improve STC by inhibiting the cAMP/PKA/AQPs signaling pathway and maintaining inflammatory/intestinal flora homeostasis.© 2023 The Authors.