Sugar-beet pulp previously heated at 110-degrees-C for 30 min was fermented at 28-degrees-C with Trichoderma reesei in the form of a semi-solid substrate, moisture level 80.0%-85.0%. The resulting product showed a 9.90% average increase in protein at the expense of cellulose and hemicellulose, which were described by 6.40% and 15.0%, respectively. The lignin and ash content of the substrate remained largely unchanged. Feed consumption, weight gain, and acceptability (palatability) trials were run with mice fed a basic &et (control, C) and with added fermented sugar-beet pulp (FSBP) at levels of 15.0% (A 1 diet) and 30.0% (A 2 &et). The mice gained weight with both test diets and with the control. Feed consumption and weight gain of mice were the same for the control diet and the A 1 diet. Feed consumption and weight gains were lower for the A 2 diet than for the control and the A 1 &ets. In free-choice feeding trials the control &et was preferred over the test diets. However, the acceptability did not differ significantly between the two test diets. Feed efficiencies (g weight gain per g feed) were not significantly different between all diets.