Abstract: The study was conducted in the Department of Animal Nutrition, Bangladesh Agricultural University with an aim to assess the degradability of crude protein (CP) and crude fibre (CF) of Jumbo grass grown in four different doses of nitrogen (N) fertilizer. The four doses of N fertilizer were 0, 50, 100 and 150 kg urea ha 1 in a Completely Randomized Design having four replications in each treatment. The unit plot size of each replicate was 4x4 m2. The fodder was harvested at the pre flowering stage at 68 days after sowing for first cutting. Four adult male cattle of about 170 kg live weight and about four years of age, fitted with permanent rumen canula, were used for the experiment. Approximately 3 g of each ground sample was placed in nylon bag separately for ruminal incubation. The size of the bag was 7x5 cm2 with pore size of 60 μ m. The bags with samples were incubated for the period of 2, 6, 12, 24, 48 and 72 h in the rumen. The bags with contents were removed from rumen and dried in an oven at 100 ° C for complete removal of moisture. The residues were analyzed for crude protein (CP) and crude fibre (CF) estimation. The disappearance values were obtained by difference in weight of the sample before and after incubation. From the percentage of disappearance data, the degradation characteristics were calculated by using the NAWAY computer programme. The results of the study showed that the effective degradability of crude protein (EDCP) of the fodder increased by increasing the N fertilizer doses while effective degradability of crude fibre (EDCF) remain unchanged. Due to fertilization the values of potential degradable fractions ‘(a+b) ’ decreases for CF and this value remain unchanged for CP. Rate constant (c value) was increased due to N fertilizer for both CP and CF.