The inherent variability of sugar industry wastewater constitutes a major challenge for the reproducibility of laboratory-scale experiments and the reliable evaluation of wastewater treatment technologies. This study presents the development of a molasses-based synthetic wastewater (MBSW) designed to provide a reproducible and representative model of sugar industry effluent under controlled experimental conditions. Unlike conventional synthetic formulations relying on simple carbon sources such as glucose, the proposed MBSW incorporates biodegradable organic matter and balanced nutrient concentrations to better reproduce the physicochemical characteristics of real agro-industrial wastewater. The synthetic wastewater was prepared by diluting raw molasses with distilled water and supplementing the mixture with nitrogen and phosphorus sources. Its physicochemical properties were characterized through measurements of pH, electrical conductivity, chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), total suspended solids (TSS), total nitrogen, and total phosphorus. The developed formulation exhibited a high biodegradable organic load, with COD values ranging from 4800 to 5050 mg/L and BOD₅ values between 2700 and 2900 mg/L, yielding a BOD₅/COD ratio of approximately 0.57. Balanced nutrient concentrations, stable conductivity values, and low variability among replicate samples confirmed the reproducibility, physicochemical consistency, and suitability of the proposed MBSW for standardized biological wastewater treatment experiments and comparative research across laboratories worldwide.