Bagasse is one of the marginal sugarcane by-products whose annual production in Iran is about 500000 metric tones. By Considering feedstuff shortage in Iran, and in order to utilize of this by-products in nutrition of fattening bulls an experiment with attention the following goals has been conducted. A: Determination of apparent digestibility, energy and other nutrients of molasses and urea-treated bagasse. B: Evaluation of urea-treated bagasse used in nutrition of fattening young-bulls as roughage. C: Determining of urea-treated bagasse on blood metabolites and estimating body composition with urea dilution technique. In the first trial two holstein male calves (400kg, BW) were used to apparent digestibility of bagasse during 21 days. Apparent digestibility and digestible energy in two methods of total fecal collection and acid insoluble ash were 55.2±1.08%, 2.15 Mcal/kg, 58.46±1.21%, 2.3. Mcal/kg respectively. In the second stage of the experiment 18 holstein males calvse including 30% alfalfa hay, 15% alfalfa plus 14% bagasse and 28% bagasse, are used for comparison.This period of trial took 128 days and calves were fed as TMR. Daily body weight gain were 1.256, 1.197, 1.19 kg/d for diets 1-3 respectively, that showes significant difference between diet 1 and diets 2, 3 (p<0.05). Mean dry matter intake and mean conversion coefficient were 6.8kg/d 5.43; 7 kg/d; 7.25, 6.14 for diets 1-3 respectively. Data analysis variance of present experiment showes that there is not significant difference among diets body composition, urea space percent, body water and fact percent equal: 31, 42, 31.22, 30.02; 52.33, 51.28, 51.8; 32.77, 30.07, 29.03; in diets 1-3 respectively.Finaly blood metabolites (Glucose -Albumin- Glubolin- Total protein- BUN-Urea) were not different significantly by different diets.