This study included three trials: 1- A laboratory experiment included twelve treatments to study the effect of using biological treatments (yeast, fungi and bacteria) on chemical composition and fiber constituents of sugar beet pulp (SBP) and olive cake (OC) to choose the best biological treatments to be use in in vitro and in vivo experiments. 2- In vitro experiment included five treatments to study the effect of control, untreated and treated SBP and OC on in vitro nutrients disappearance, T(1):Concentrate feed mixture (CFM) + berseem hay (BH) (control). T (2): CFM contains (40% untreated SBP + 30% untreated OC) + BH. T(3): CFM contains (40% SBP + 30% OC) treated with S. cerevisiae+ BH. T (4): CFM contains (40% SBP + 30% OC) treated with T. viride+ BH and T (5): CFM contains (40% SBP + 30% OC) treated with C. cellulasea+ BH. 3- In vivo experiment to study the effect ofthose experiments on sheep digestibility coefficients, rumen fermentations, microbial protein, rumen microbes and some blood parameters. The results revealed a significant improvement (P≤0.01) in CP content and a significant reduction in CF and NDF content with biological treatments. Digestibility coefficients and nutritive values were increased (P≤0.01) in treated groups, also, nitrogen balance was enhanced (P≤0.01) than untreated group. Rumen fermentations and microbes showed significant increase (P≤0.01) in treated groups. Serum total protein, albumin and globulin concentrations were more in treated groups, although they reduced urea concentration, GOT and GPT activity.