Our objective was to evaluate the effect of supplementation with live yeast (Saccharomyces cerevisiae CNCM I-1077) on feed intake and rumen parameters of beef cattle. Eight rumen cannulated steers with 24 mo and weighting 450 kg were used in a duplicated 4x4 Latin square design. Two levels of concentrate (60 or 80% of DM) and 2 treatments (with or without yeast supplementation) were applied, having sugarcane silage as the roughage source. The product was given in capsules, via rumen cannula, to achieve 8 × 10⁹ cfu of yeast per animal. Animals were housed individually in tie-stalls with free access to water, and fed ad libitum allowing for 5 to 10% of orts. Feed was offered twice daily and orts weighed daily to measure DMI. Each period lasted for 28d to allow for complete washout of the previous treatment. The last 2 d of each treatment period were used for rumen fluid sample collection for pH and short chain fatty acids (SCFA) measurements. Feeding diets with 80% concentrate increased feed intake (9.4 vs. 8.6 kg ± 0.4, P = 0.05); however, yeast supplementation had no effect on feed intake. Feeding a greater concentrate diet decreased mean rumen pH (6.52 vs. 6.69 ± 0.07, P < 0.01), and live yeast supplementation prevented the drop in rumen pH. Feeding the greater concentrate diet increased rumen total concentration of SCFA (43 vs. 36 mM ± 3, P = 0.03), but only without yeast supplementation. Supplementation with live yeast increased the molar proportion of acetate (63.2 vs. 62.4% ± 0.8, P = 0.03), and of valerate (1.23 vs. 1.18% ± 0.06, P = 0.06) in the rumen, and decreased the concentration of butyrate (10.6 vs. 11.4% ± 0.5, P = 0.03). Yeast supplementation promoted changes in rumen fermentation that are associated with better maintenance of a higher pH, and a higher proportion of acetate in the rumen. However, these changes did not translate into a detectable increase of feed intake.