Berberine and metformin, both established pharmaceutical agents with herbal origins, have incidental beneficial effects on multiple diseases, including diabetes. These effects have been speculated to occur via the gut microbiome. In this study, we administered either berberine or metformin to db/db mice and investigated changes in body weight, food intake, and blood glucose levels. Fresh stool samples were analyzed using 16 s rDNA high-throughput sequencing to evaluate the gut microbiome. Short-chain fatty acids (SCFA) in the stool were quantified using gas chromatography. The expression of NF-κB signaling pathway and tight junction (ZO1 and occludin) proteins in the intestinal epithelium was determined using qPCR and western blotting. The intestinal barrier structure was examined using transmission electron microscopy and serum lipopolysaccharide (LPS) was measured using a commercial kit. Both berberine and metformin reduced food intake, body weight, and blood glucose and HbA1c levels. Both treatments effectively restored the intestinal SCFA content, reduced the level of serum LPS, relieved intestinal inflammation, and repaired intestinal barrier structure. Intervention with metformin or berberine modified the gut microbiome in db/db mice, increasing the number of SCFA-producing bacteria (e.g., Butyricimonas, Coprococcus, Ruminococcus) and reducing opportunistic pathogens (e.g., Prevotella, Proteus). An increased abundance of other probiotics including Lactobacillus and Akkermansia was also observed. Berberine and metformin can modulate the composition of the gut microbiome and reduce body weight, blood glucose levels, and intestinal inflammation in db/db mice, which demonstrates their effectiveness in the reduction of diabetic complications in this model.