In this study three experiments were conducted, the 1^st (a laboratory experiment) included nine treatments (T1-T9) to study the effect of using biological treatments (fungal, bacterial, yeast or yeast combined with fungi or bacteria) on chemical composition and fiber constituents of sugar beet pulp (SBP) to choose the best biological treatments for testing in the 2^nd experiment (in vitro experiment). In the 2^nd experiment, seven rations containing the best five biologically treated SBP as well as control and untreated SPB rations were used to study the effect of the experimental rations on in vitro chemical composition and nutrients disappearance. These rations included R1 (control): concentrate feed mixture (CFM) + berseem hay (BH); T2: CFM + untreated SBP+ BH; T3: CFM + SBP treated with S. cerevisiae+ BH; T5: CFM + SBP treated with T. viride + BH; T5: CFM + SBP treated with T. viride + S. cerevisiae + BH; T6: CFM + SBP treated with C. cellulasea + BH, and T7: CFM + SBP treated with C. cellulasea + S. cerevisiae + BH. In the 3^rd experiment (digestibility experiment) was carried out to study the effect of feeding the same rations on digestibility coefficients, rumen fermentations parameters, microbial protein, protozoal count, number of total bacteria and cellulolytic bacteria and some blood parameters of adult rams. Results revealed that biological treatments increased (P<0.05) CP content and decreased CF, NDF, ADF, ADL content. Digestibility coefficients, concentrations of total volatile fatty acids (TVFA's), total nitrogen, true protein, microbial protein and microbial count increased (P<0.05), nitrogen and water balances improved (P<0.05) in biologically treated SBP as compared to control and untreated SBP rations.