The aim of this research was to assess the impact of different combinations of chemical nitrogen fertilizer levels and red yeast as a biofertilizer (F₁,100 kg N+ red yeast; F₂, 75kg N+ red yeast; F₃,50kg N+ red yeast;F₄, 25kg N+ red yeast; F₅, unfertilized N+ red yeast and F₆,100kg N without red yeast) on microbial biomass carbon and nitrogen, growth characteristics, yield and its components as well as harvest index of four durum wheat cultivars (V₁, Beni-swif 5; V₂, Beni-swif 1; V₃, Sohag4; V₄, Sohag5). Results confirmed that, different wheat cultivars exhibited a significant effect on most studied traits in both seasons. V₁ surpassed all tested cultivars for most studied traits followed by V2, meanwhile, V4 ranked the last one for most traits in both seasons. The combination of all chemical nitrogen fertilizers with red yeast possessed a highly significant effect on all studied characteristics. Significant interactions were recorded between cultivars and different combinations of yeast and nitrogen fertilizer levels on wheat yield and its components during both seasons, V₂×F₂ and V₂×F₁ obtained the greatest biological yield of 7.89 and 7.40 ton/fed. and grain yield of 20.75 and 20.49 ardab/fed in the first and second seasons, respectively. Grain yield (ardab/fed.) was highly positive and significantly correlated with all studied traits in both seasons. In conclusion, applying red yeast as a promising biofertilizer with different chemical nitrogen fertilizer rates could be recommended because it significantly increased the microbial biomass and, achieved a highly significant wheat yield, while reducing chemical fertilizers consumption.