Effects of processing technologies and cell wall degrading enzymes on in vitro degradation of barley were tested in a 5 × 2 factorial arrangement: 5 technologies (unprocessed, wet-milling, extrusion, autoclaving, and acid-autoclaving), with or without enzymes. Upper gastrointestinal tract digestion (Boisen incubation) and large intestinal fermentation (gas production technique) were simulated in duplicate. All technologies increased digestion of DM (13 to 43% units) and starch (22 to 51% units) during Boisen incubation, compared with the unprocessed control (P < 0.01). Wet-milling, extrusion, and acid-autoclaving increased CP digestion by 29 to 33% units (P < 0.01). Xylanase and β-glucanase addition increased digestion of DM (≈ 20% units), starch (≈ 20% units), and CP (≈ 10% units) in unprocessed and autoclaved barley (P < 0.01). Wet-milling, extrusion, and acid-autoclaving, reduced the extent (50%) and maximum rate (60 to 75%) of fermentation (P < 0.01), which appeared to reflect the reduced amount of starch present in the Boisen residues. In conclusion, wet-milling, extrusion, and acid-autoclaving improved in vitro starch and CP digestion in barley, which is related to the cell wall matrix disruption. Addition of xylanases and β-glucanases improved in vitro starch and CP digestion only in unprocessed barley or barley poorly affected by processing.