ABSTRACT This investigation was conducted for two 2016-2017 and 2017-2018 seasons at  Agric. Res. Station (30° 02' N latitude and 31° 13' E longitude, altitude 22.50 m above sea level), Giza, Egypt, to study the response of fodder beet (Beta vulgaris) c.v. Voroshenger to partial substitution of mineral N fertilizer by bio-fertilizer (full recommended dose of mineral N fertilizer, 75% RD of mineral N fertilizer +bio-fetilizer , 75% RD of mineral N fertilizer, 50% RD of mineral N fertilizer + bio-fertilizer, 50% RD of mineral N fertilizer and bio-fertilizer).The experiments were laid out in a complete randomized block design with three replicates and could be results summarized as follows:- Applying bio-fertilizer with 75% RD of mineral N fertilizer increased root diameter, root and shoot length, plant height, fresh and dry of shoot and root yields fed^-1, crude protein content and digestible crude protein and CF yields. N, P, K% and their uptake were increased as a result of fertilizer application (75 % RD of mineral N fertilizer + bio-fertilizer) in both seasons. In respect to the enzymatic activities, nitrogenase enzyme activity of two seasons significantly increased as a result of inoculation + 50% of the full recommended rate of mineral N fertilizer. While, dehydrogenase activity and population density of tested bacteria in the rhizosphere were significantly increased by applying biofertilizer + 75% RD of mineral nitrogen fertilizer n. Moreover, inoculation with the used biofertilizer led to significant increases the population density of tested bacteria in the rhizosphere of this plant. The highest gross margin (GM) was achieved from the treatment T₂ (75% RND mineral fertilizer with bio- fertilizer) compared with other treated treatments in both seasons. In addition, the use of bio-fertilizer reduces the environmental pollution.