This research was conducted to detrmine the effect of seeed rates in mixtures of Pea + Oat on the green forage and silage proein fractions by Cornell Net Carbohydrate and Protein System (CNCPS). Experiment was established in autumn in 2012, on October the 20th and plant samples were taken in spring 2013 at forming the first pods on 2/3 plants of Pea at Institute for forage crops, Kruševac, R Serbia, using five different mixture rates of Pea and Oat crops (100% Pea + 0% Oat; 0% Pea + 100% Oat; 25% Pea + 75% Oat; 50% Pea + 50% Oat and 75% Pea + 25% Oat). Pea:Oat mixtures were treated with bacterial inoculant and ensiled in anaerobic jars for 45 days. Green forages and silage samples were analysed for DM (Dry Matter), CP (Crude Protein), primary protein fractions – TP (True Protein), NPN (Non Protein Nitrogen), IP (Insoluble Protein), SolP (Soluble Protein), NDICP (Neutral Detergent Insoluble Crude Protein) and ADICP (Acid Detergent Insoluble Crude Protein) and protein fractions by CNCPS. An analysis of variance found statistically significant differences among mixture rates for all variables, except IP and SolP. Silage from monoculture Pea had the highest NPN (696.2 g kg-1 CP) and SolP (713.8 g kg-1 CP), followed by the mixture of Pea with Oat 75:25 (662.5 and 653.4 g kg-1 CP, respectively). On analyzing the CNCPS protein fractions of Pea:Oat silages, it was found that silage from Pea monoculture contained the highest PA fraction and that PA fraction increased with increasing Pea ratios in silages, which was direct reflection of their high NPN and SolP in green forages and in silages. Becouse of those facts 25:50 and 50:50 Pea:Oat mixtures silages could be recomended for ruminant nutrition. Bacterial inoculant evaluated can increase the TP content, as well as PB1 and PB3 fractions.