The gut microbiota can act as a buffer against changes in energy and food availability and adapt plastically to fluctuations in the host's diet. However, it is unknown how changes in the gut microbiome with the seasons impact microbial metabolism and the accessibility of nutrients to hosts. The study utilized 16S rRNA and UHPLC-MS/MS approaches to examine seasonal fecal metabolome variations in the captive Yangtze finless porpoises (YFPs) to determine if these variations are linked to nutrient intake or gut microbiome composition changes. The YFPs were mostly fed a frozen and live fish diet, with different food intakes yearly. We found that gut microbial diversity remained constant, but community structure varied seasonally. Firmicutes and Cyanobacteria were higher in winter, Actinobacteria in spring and fall, and proteobacteria in summer. The genus Paeniclostridium was significantly higher in the spring season, Romboutsia and Clostridium_sensu_stricto_13 were significantly higher in the summer, while Terrisporobacter and Macrococcus were significantly higher in the fall group. The study reported that seasonal dietary variation significantly impacted the fecal metabolome by affecting the metabolism, including energy, amino acid, carbohydrate, and nucleotide metabolism of the captive YFP. Moreover, significant correlations between metabolome and microbiome were found, and these correlations may indicate that the captive YFP has adapted to cope with dietary variations and enhance energy acquisition. These findings improve our knowledge of the link between microbiota, diet, metabolites, and the physiology of the host and suggest that gut microbial populations may adapt continuously to changes in diet.