Sugarcane bagasse and rice husk are lignocellulose rich agricultural by-products designated as an alternative feed for ruminant. However, their nutritive value is relatively low due to low digestibility, high fiber content, low protein content and low palatability. Therefore, the nutritional value of these by-products can be improved with biological treatments. The objective of this study to evaluate the feed intake, digestibility, growth performance and blood profile of Hararghe highland sheep fed biologically treated rice husk (RH) or sugarcane bagasse (SCB) in concentrate mixtures. Thirty six rams with an average age of 10 months and an average initial weight of 18 +/- 1.8kg were assigned in randomized complete block design (RCBD) in 2 x 3 factorial arrangements, with two feeds (SCB and RH) and three treatment groups (Control, Trichoderma viride and effective microorganism (EM)). 5\% EM1 was used to prepare the activated EM solution and 5\% Trichoderma viride (Tv) solution was used to prepare inaculant. Sheep were fed ad libitum for 90 days at 20\% refusal rate followed by10 days of digestibility trial. Nutrient intake and digestibility of sheep were significantly (p < 0.05) affected by the interaction. Sheep fed either treated or untreated rice husk based diets had significantly higher dry matter (DM g/d), organic matter (OM g/d), crude protein (CP g/d) and metabolizable energy (ME MJ/d) intake than a diet based on untreated sugarcane bagasse or treated with Trichoderma viride. Sheep fed diets containing either treated or untreated rice husks had a higher average daily weight gain (ADG) and feed conversion efficiency than sugarcane bagasse containing diets. Sheep fed diets containing biologically treated roughages had significantly higher (p < 0.05) average daily weight gain and feed conversion efficiency. Conversely, no significant differences were observed between rams fed diets containing EM and Trichoderma viride (Tv) treated rice husk or sugarcane bagasse in average daily weight gain (ADG) and feed conversion efficiency (FCE). Values of some blood hematology (red blood cell, haemoglobin and packed cell volume) and total protein, urea, glucose and cholesterol of serum me-tabolites were significantly (p < 0.05) higher for rams fed diet containing rice husk. In conclusion, the results show that the biological treatment of feed with the effective microorganism or Trichoderma viride improved nutrient utilization and average daily gain in the sheep fattening diet.