Soluble fiber can be fermented by microflora in the colon resulting in short-chain fatty acid (SCFA) production. SCFA can be used as an energy source for the host, enterocytes, colonocytes, and immune cells, supporting cell differentiation and gut health. An in vitro model has been used to predict the colonic fermentability of fibers. Whole soybean (WSB) contains oligosaccharides and non-starch polysaccharides that may behave as beneficial fermentable substrates. The objective of this study was to determine the effect of WSB oligosaccharides on in vitro fermentation using dog feces as inoculum. Treatments included total dietary fiber residues from WSB, soy hull (SH), pea fiber (PF), beet pulp (BP), soybean oligosaccharides (WSBOS), and raffinose, stachyose, and verbascose (WSBRSV). The fecal samples were collected from three Beagle dogs and maintained in anaerobic conditions until dilution and substrate inoculation. Test tubes containing enzymatic pretreated fiber sources and inoculum were incubated for 1, 2, 4, 8, and 12 hours at 39°C. Organic matter disappearance (OMD), pH, and SCFA were determined for each fiber source and time point. The data were subjected to ANOVA using the general linear model procedure (SAS, v 9.4). Least square mean differences were assessed using Tukey’s post hoc test. WSBOS and WSBRSV had greater OMD and butyrate than BP (P < 0.05; 43.59 and 60.18% vs 40.96% OMD; 293.33 and 266.67 vs 130umol/g, respectively). BP and WSBRSV had the lowest pH (6.66 and 6.74, respectively) at 12 h (P < 0.05). WSB had similar butyrate compared with BP (average 118umol/g). PF and SH were poorly fermented with the least OMD (18.59% and 20.45%, respectively) and butyrate (46.67umol/g and 66.67umol/g, respectively) compared with other fiber sources.