Abstract: The present experiment was conducted to apply Solid State Fermentation (SSF) for protein enrichment using Sweet Orange (SWO) and Orange Pulp (OPW) wastes by Aspergillus niger isolate No. 5, isolated from Addis Ababa city wastes. The total proteins were extracted to estimate the mycelial biomass from the seven days growth of fungal mold which have grown on orange wastes (SWO and OPW). Sodium hydroxide and phosphate extraction buffers and other growth factors i.e., moisture 60%; temperature, at 30°C; pH at 7.00 and inoculum size 106 spores mL-1 were found to be most efficient for the extraction of the proteins using the substrates by Aspergillus niger isolate No. 5. The maximum protein enrichment of SWO (45.56%) and OPW (47.48%) were obtained at 30°C. The highest protein enrichment 50.84% using substrate SWO was attained at pH 7. The effect of supplementation of the nitrogenous sources on the final biomass was compared with control. The result of using sodium hydroxide (NaOH) buffer has shown that 5 g of substrates, squeezed Sweet Orange Wastes (SWO) and Orange Pulp Wastes (OPW) were produced maximum protein level 23.93 and 23.59% and utilized by Aspergillus niger isolate No. 5 at 106 spores mL-1 inoculum (W/W) protein, respectively.