Processing of dark tea varieties, such as Fu brick tea, Liupao tea, Qianliang tea, and Qing brick tea, includes solid-state fermentation involving microorganisms. In this study, we analyzed the major chemical constituents of dark tea extracts and evaluated their modulatory effect on the gastrointestinal function in normal mice, including the improvement of gastrointestinal transit and intestinal microbial, as well as the attenuation of intestinal microbial dysbiosis and intestinal pathological damage, and the adjustment of immune function in antibiotic-treated mice. Substantial differences in major chemical constituents, including total polyphenols, total organic acids, water extract content, 18 free amino acids, gallic acid, and six tea catechins, were observed among Fu brick tea, Qianliang tea, Qing brick tea, and Liupao tea extracts. Extracts from the four dark tea varieties significantly promoted gastrointestinal transit and colonization of beneficial Bifidobacterium and Lactobacillus, and inhibited the growth of harmful Escherichia coli and Enterococcus in normal mice. In addition, Qianliang tea, Qing brick tea, and Liupao tea extracts significantly accelerated the reversal of the ampicillin sodium-induced pathological damage in the ileum, intestinal bacterial dysbiosis (Bifidobacterium, Lactobacillus, E. coli, and Enterococcus), and low immunity.