An experiment was conducted to determine the effects of soluble to insoluble fiber ratios on the intestinal viscosity, organ growth, intestinal morphology, and nutrient digestibility. A total of 432 one-day old Cobb® male broilers were randomly assigned to six dietary treatments and reared to 21 days of age in battery cages (n=6 replicates per treatment). A semi-purified basal diet with 0% crude fiber was formulated to which the adequate soluble to insoluble fiber ratio was added. All birds were fed a common corn-soybean meal diet during the first 7 days to ensure proper organ growth development, before being exposed to the semi-purified experimental diets. Growth performance was measured on days 14 and 21. Ileal samples were collected on days 14 and 21 for analyses of intestinal viscosity. On day 21, ileal digesta were collected from 7 birds per replicate for nutrient digestibility analyses, and one bird was used to collect sections of the duodenum, jejunum, and ileum for intestinal morphology analyses. Higher soluble to insoluble fiber ratios resulted in poorer gain per bird and feed efficiency from d 7 to 21 (P < 0.01). No statistical differences were observed in the organ growth among the dietary treatments (P > 0.05). No differences in the duodenal villus to crypt ratio were observed among the dietary treatments (P > 0.05). However, the group fed the lowest soluble to insoluble fiber ratio had the smallest villus to crypt ratio, and the biggest ileal villus to crypt ratio (P < 0.001). Decreases in digestibility of dry matter, apparent metabolizable energy and crude protein were observed in increases in the soluble to insoluble fiber ratio (P < 0.05). No statistical differences in intestinal viscosity were observed from d 7 to 14 (P > 0.05). However, higher soluble to insoluble fiber ratios resulted in higher intestinal viscosity on day 21 (P = 0.09).