The objective of this study was to evaluate the in situ NDF digestibility of corn stover treated at ambient temperature with a solution of sodium hydroxide and ethanol co-solvent. The treatment process is patented by Cellulose Sciences International (CSI) of Madison, WI. Digestion kinetics were evaluated in situ for untreated corn stover, corn stover treated with CaOH at 70g kg⁻¹, corn stover treated by the CSI process and untreated soyhulls. All materials were ground through a 2 mm screen in a Wiley mill and 0.5 g was sealed into Ankom F57 bags. Bags were placed in the rumens of 2 fistulated cows for 0h, 12h, 24h, 30h, 36h, 42h, 48h, 96h, 120h, and 240 h in reverse order. Bags were then washed, dried and contents analyzed for residual NDF. The 240h time point was used as the estimate of indigestible NDF (iNDF). The rate of digestion of potentially digestible NDF (pdNDF) was determined from the slope of the natural log of the pdNDF residue verses time. The fraction of iNDF and the rate of pdNDF degradation between forages were compared by ANOVA (PROC Mixed, SAS, v 9.3) as a randomized design with cows as replicates. Least square treatment means were compared by PDIFF. The digestion rate of pdNDF (kd,) of CSI-treated corn stover (5.36%/h) was higher than CaOH-treated stover (2.27%/h, P < 0.01), and untreated corn stover (1.76%/h, P < 0.001). The kd of soyhulls (4.93%/h) was similar CSI-treated stover (P = 0.56). The iNDF proportions in CSI-treated stover and soyhulls, were similar (2.8 and 3.6% of NDF, respectively, P = 0.26). The CSI-treated stover had lower iNDF than CaOH-treated stover or untreated stover (2.8, 27.3 and 35.1% of NDF, respectively, P < 0.0001). Results indicate that the CSI-treatment process improved rate and extent of digestion of corn stover to a greater degree than the CaOH treatment process. The CSI treatment process appears to convert corn stover into a source of highly digestible fiber with digestion characteristics similar to soyhulls.