Background:This study aimed to investigate the impacts of guar gum and cellulose as the source of dietary fiber during gestation on the reproductive performance of sows. Methods:A total of 210 sows (parities 3–6) were randomly allocated into six diets (n=35) throughout gestation to feed graded levels of dietary fiber (DF), including a corn-soybean meal-based control diet with no wheat bran inclusion (CON, 12.5％DF), a wheat bran-rich diet (DF1, 17.4％DF), and another 4 diets (DF2, 17.7％DF;DF3, 18.1％DF;DF4, 18.4％DF;DF5, 18.8％DF) in which wheat bran were equally substituted by 1％, 2％, 3％and 4％purified FIBER MIX (guar gum and cellulose, 1:4). All sows received similar DE and other nutrients throughout gestation. Results:DF treatment during gestation resulted in normal fecal score (1 to 5 with 1=dry and 5=watery) in sows compared with those received the CON diet (P< 0.05). The number of total born piglets had a tendency to be affected by dietary treatment (P=0.07), and correlation analysis revealed a linear response of total born to dietary fiber levels during gestation (P<0.01). Sows received the DF2, DF3, and DF5 diets during gestation had a greater ADFI during lactation compared with those in the CON group (P<0.05) without affecting the daily body weight gain of suckling piglets. Gut microbiota compositions were dramatically changed by the gestation stage and some of those were changed by DF inclusion. Fecal acetate, propionate, and butyrate of sows were markedly increased in late gestation, and butyrate contents in feces of gestating sows were significantly affected by DF levels (P<0.01). Serum concentrations of pro-inflammatory TNF-αwere decreased and anti-inflammatory IL-10 was increased on day 30 of gestation by DF levels (P<0.05). Conclusions:In summary, increasing dietary fiber levels by guar gum and cellulose during gestation improved the reproductive performance of sows, which might be related to changes in immunity and gut microbiota of sows.