Biowastes (BW), the main raw materials for the composting installations in developing countries, are characterized for containing uncooked food wastes (FW), high moisture content, low porosity, acidic pH, and low C/N ratios which affects the overall composting process (CP). In this study, we evaluated the effect of adding sugarcane bagasse (SCB) and star grass (SG) (Cynodon plectostachyus (K. Schum.) Pilg.) as bulking materials (BM) over the quality of the substrate, progress of the process, and quality of the obtained product. In this sense, two pilot-scale experiments were performed. The first one contained a substrate formed by 78% BW and 22% SCB (pile A). The second experiment contained a substrate formed by 66% BW and 34% SG (pile B). For each experiment, control treatments (piles A’ and B’ respectively) were performed by using 100% BW without BM. The results showed that in both cases the adding of BM improved substrate quality (pH, moisture, and total organic C content [TOC]), speeding up the starting step (2-3 d) and reducing the duration of the thermophilic phase of CP (3 d). However, the physico-chemical properties of both BM increased cooling and maturation phases duration (between 15 and 20 d). Obtained products quality was improved in terms of higher TOC, cation-exchange capacity, bulk density, and higher water holding capacity. Application of obtained products A and B could improve some soil properties like major nutrient, water retention, and increasing the organic matter.