Fodder is the mainstay of ruminant production in majority of developing countries. However, its low yield and poor quality are considered considerable constrains which impede ruminant productivity. Fodder production and its nutritive value can be enhanced by ensuring adequate supply and utilization of nutrients in plant growth which is generally hampered by decreased or imbalanced proportion of P and/or nitrogen (N). The study was planned to examine the influence of phosphorus application with or without nitrogen on nutritive value and in situ digestion kinetics of oat (avena sativa) grass in Nili Ravi buffalo bulls. Nutritive composition data were analyzed by completely randomized design while in situ digestion kinetics data were analyzed by 4x4 latin square design using the general linear model. Oat grass seed was sown in lines using standard agronomic practices. The P fertilizer was applied at the rate of 0, 10, 15, 20, 25 and 30 kg/acre and treatments were denoted as control (C), P10, P15, P20, P25 and P30, respectively. Likewise, in independent fields along with P,  N in an equal amount of P was also applied and treatments were represented as C, PN10, PN15, PN20, PN25 and PN30, respectively. Each treatment was applied on two hectares which were equally divided into three parts to serve as replicates. The dry matter (DM) and crude protein (CP) of oat fodder increased with increasing application of P with or without N. Findings of in situ nutrient digestibility indicated that rate of disappearance and extent of digestion of DM, CP, neutral detergent fiber (NDF), acid detergent fiber and hemicellulose increased. However, NDF and hemicellulose and lag time decreased with increasing application of P with or without N. Outcome of the study imply that nutritive value of oat grass increased with increasing P supplementation and similar observations were noticed for nutrient digestibility and rate of disappearance with or without N in buffalo bulls.