Sugarcane bagasse (SB) is a low-quality roughage source that is often plentiful during times of forage shortage. It is generally less costly compared with other conventional sources of forage. We hypothesized that SB could be used as a source of roughage for dairy cattle by replacing wheat straw (WS), another low-quality forage. This study evaluated the effects of replacing WS with SB in diets offered to mid-lactation dairy cows on milk production and fatty acid profile, intake, digestibility, chewing activity, and ruminal fermentation. Nine multiparous Holstein cows averaging (mean +/- standard deviation) 105 +/- 12 d in milk, 42.1 +/- 2.9 kg of milk/d, and 617 +/- 59 kg of body weight were used in a replicated 3 x 3 Latin square with 21-d periods. Treatments were (\% of dietary dry matter, DM): (1) 0SB, diet containing 0\% SB and 27\% WS, (2) 9SB, diet containing 9\% SB and 18\% WS, and (3) 18SB, diet containing 18\% SB and 9\% WS. Sugarcane bagasse had greater organic matter (OM; 94.1 vs. 85.1\% of DM), neutral detergent fiber (NDF; 86.2 vs. 76.4\% of DM), acid detergent fiber (ADF; 62.9 vs. 45.2\% of DM), and lignin (19.9 vs. 10.3\% of DM) concentration, but less crude protein (CP; 2.63 vs. 3.72\% of DM) concentration than WS. Sugarcane bagasse also had greater physically effective NDF (total dietary NDF multiplied by \% of TMR on the 8-mm + 19-mm sieves, peNDF8; 63.2 vs. 40.6\% of DM) and undegraded NDF after 288 h of incubation (uNDF288; 35.5 vs. 21.2\% of DM) contents than WS. The undegraded NDF after 30 h of incubation (uNDF30) content was similar for all diets; however, peNDF8 concentration and proportion of long particles (retained on a 19-mm sieve) increased linearly as SB inclusion in the diets increased. Cows in- creasingly sorted against long particles as SB replaced WS. Intakes of DM (26.53 kg/d) and NDF (8.58 kg/d) did not differ among the treatments, but intakes of OM and CP decreased, whereas ADF and uNDF288 intakes increased with SB inclusion level. Total-tract digestibilities of OM, CP, and NDF decreased linearly as SB replaced WS. Milk yield (37.0 kg/d), energy-corrected milk yield (ECM; 38.2 kg/d), feed efficiency (1.44 kg ECM yield/kg DM intake), and milk composition (fat, 3.89\%; true protein, 2.90\%) did not differ among diets. Increasing SB concentration of the diet linearly increased rumination time, but ruminal pH (ruminocentesis, 4 h after feeding) decreased. Total volatile fatty acid concentration increased linearly, whereas acetate: propionate decreased linearly, as SB replaced WS. The results indicate that replacement of WS with increasing levels of SB in low-forage diets with similar uNDF30 concentrations did not affect performance of mid-lactation dairy cows. We conclude that SB can be used as a fiber source in diets fed to dairy cows in mid-lactation; however, the decrease in total-tract digestibility of diets may decrease lactational performance when fed to highproducing dairy cows.