Two field experiments were conducted in 2019 and 2020 seasons at Desert Research Center, Mataria, Cairo, Egypt, and its experimental farm at Ras Sudr Experimental Station in South Sinai, in cooperation with the Department of Horticulture, Faculty of Agriculture Benha University, to study the effect of biogas slurry fertilizer and natural extracts on biomass, chemical constituents, and quality of Stevia rebaudiana L. plant.  Results showed that biogas fertilizer along with the different natural extracts exerted a significant influence on yield, chemical constituents, stevioside and rebaudioside A., of stevia. The highest values in most of the parameters i.e. shoot fresh and dry weights biomass, leaves fresh and dry weights biomass, N, P, K and pigments in the first cut by recommended dose of chemical fertilizer (T₁) combining with garlic as drench addition, Yucca extract as a foliar spray or Azolla extract as drench addition (M₄, M₅ or M₂,respectively). On the other hand, the second cut took the same line as the first cut but with 50% NPK + 5000 kg h^-1 (T₃) as either garlic extract or Azolla extract as drench addition (T₃×M₄ or T₃×M₂) as registered the highest values of parameters mention before in most cases. As for the highest values of stevioside and total stevioside content were recorded by 50% NPK + 3000 kg h^-1 combining with Azolla aqueous extract as drench addition (T₄×M₂). Rebaudioside A., registered by combination of the recommended dose of biogas fertilizer and yucca aqueous extract as a foliar spray (T₂×M₅). Conclusively, the use of half (50%) of the recommended dose of chemical fertilizer with its equivalent of the recommended nitrogen dose and replaced with biogas fertilizer, in addition to the use of both extracts of Azolla and garlic as a drench addition, led to reducing nitrate accumulation as a problem of the use of chemical fertilizers on the human health and economic damages.