The present study aimed to investigate the effects of adding xylanase enzyme (XY) to a basal diet containing 300 g maize stover and 700 g concentrate/kg dry matter (DM) on feed intake, ruminal fermentation, total tract and ruminal digestibility, as well as some blood parameters. Four male Rambouillet sheep (39 ± 1·8 kg body weight), with permanent rumen and duodenum cannulae were used in a 4 × 4 Latin square design. Sheep were fed a basal diet without xylanase addition (control, XY0), or with the addition of xylanase at 1 (XY1), 3 (XY3) or 6 (XY6) μl/g of diet DM for 84 days, with four 21-day experimental periods. Feed intake, digestibility and rumen fermentation parameters were determined on days 16–21 in each experimental period, and the apparent ruminal neutral detergent fibre (NDF) digestibility was determined on days 16 and 17. Treatments XY1 and XY3 increased feed intake, whereas digestibility was increased with XY6. Ruminal NDF digestibility increased when sheep were fed diets treated with xylanase. Ruminal pH, ammonia-N and acetic acid increased with xylanase treated diets. Propionic acid concentration increased with diet XY1 at 3 h post-feeding, but after 9 h post-feeding its concentration decreased in the rumen of sheep fed xylanase treated diets. Xylanase had no effect on blood urea, phosphorus and triglycerides. Addition of xylanase at 6 µl/g DM in a diet containing 300 g maize stover and 700 g concentrate/kg DM and fed to Rambouillet sheep improved feed digestibility and ruminal fermentation without affecting blood parameters.