Reuse of sludge from a water treatment plant and fly ash for the manufacturing of adobe brick is a feasible approach for practical applications due to the numerous benefits from the cost savings of construction materials and the reduction of environmental pollution. In this study, sludge from a groundwater treatment plant and fly ash from a thermal power plant were used as alternative aggregates to replace clay, a traditional component for brick making. The main objective of this study is to produce adobe bricks by using hydraulic press technology. The optimum aggregate composition was investigated by determining the compressive strength according to Vietnam national standard TCVN 6355:1-2009. Other supplementary materials, including cement, liquid glass, and polypropylene fibers, were used as additives and adhesives. Results showed that a 2-hole brick product (8 × 4 × 8 cm) with strength M 4.0 satisfied the national quality standard, TCVN 6477-2016. In addition, the aggregate composition (wt%) as sludge: cement: fly ash: polypropylene fibers of 50 : 35: 15 : 0.5%/m3 aggregates was found to be the optimum ratio. This product shows a medium compressive strength that is appropriate in the construction of walls or fences in industrial factories or households. The results obtained in this study show a promising approach for the brick-making industry in Vietnam. A large amount of sludge can be reused as an alternative material to reduce the product price and achieve natural resource conservation.