Background Given that approximately 70% of immune cells reside in the gastrointestinal tract, modulation of the intestinal microenvironment has emerged as a promising strategy for immune regulation. Dietary fibers alter the gut microbiota and are fermented to produce metabolites that influence host immune responses. Here, we investigated the effects of different dietary fibers on the intestinal microenvironment and immune cell populations. Methods C57BL/6J mice were fed diets containing 5% cellulose (CE) as a control or 2.5% corn arabinoxylan (CX), wheat bran arabinoxylan (WX), or partially hydrolyzed guar gum (PHGG), with the remaining 2.5% CE to maintain a total dietary fiber content of 5%. Fecal SCFAs, gut microbiota, and colonic immune cell populations were analyzed. In vitro experiments were also performed to investigate the effects of these fibers on T-cell differentiation. Results WX or PHGG supplementation significantly increased fecal butyrate concentrations and colonic Treg frequencies, whereas CX and PHGG increased colonic Th17 cell frequencies. As the mechanism underlying Th17 induction remained unclear, in vitro assays were performed. Dietary fibers alone did not induce Th17 differentiation, whereas fecal suspensions from CX- or PHGG-fed mice significantly promoted Th17 differentiation compared with those from CE-fed mice. These findings suggest that CX and PHGG promote colonic Th17 cell induction through alterations in the gut microbiota and/or their metabolites.