Agro-industrial sectors in Ethiopia are highly expanding and exposing environmental burden for ecosystem due large volume sludge accumulation. On one hand, sludge generated from brewery waste treatment plants are recognized as good alternative options for agricultural reuse. Compost originating exclusively from food industry biosolids used as organic fertilizer according to European legislation. The main purpose of this research study was investigating the potential of an aerobic composting process for the Preparation of Biofertilizer from Brewery Wastewater Sludge and spent brewery diatomaceous (Kieselguhr) sludges. In this study, sludge derived from a brewery sludges was mixed with spent brewery kieselguhr sludges and, yielding three different mixtures to be composted. The composting process was assessed through measurements of temperature, moisture, pH, electrical conductivity, organic carbon, organic nitrogen, and total organic phosphorus. Moreover, the total concentration of heavy metals (Cr, Cu, Cd, Hg, and Pb) and the plant nutrients (Na, K, Mg, Ca, and Fe) was determined in at the end of each compost process. Additionally, the degradation degree was evaluated through the detection and quantification of E. coli, Salmonella, and Fecal Coliform. It was found the ratio of C/N was 9:1 and phosphorus fluctuated around 8.5 %. Cr, Cu, Cd, Hg, and Pb were found 1.95±0.045, 5.36±0.03, 0.475±0.004, 0.165±0.004 and 0.273±0.005 mg/Kg respectively. Plant Nutrients including Na, K, Mg, Ca and Fe were 100.16 g/kg, 122.95, 869.92, 4084.08 and 26.86 mg/kg respectively. The result revealed that the compost sludge has high organic matter and phosphorous content that fulfills the suggested Ethiopian standards for the fertilizer value of compost sludge. Optimum pH and EC values, substantial qualities of nitrogen and high WHC and large secondary plant nutrients (Ca, Mg, K and Na) that suggested that, all able to contribute beneficial improvement of soil properties. BWS and BSDS yielded composts of acceptable quality due to low metals concentrations in the final compost in line with EPA standard value limits. The higher pathogen (E. coli, Salmonella, and Fecal Coliform) contents of raw sludges, which are stabilized in composting to the required standards and it was found far below the upper EPA standard limits for unrestricted reuse of compost sludge for agricultural application.