Stillage, a byproduct resulting from the distillation of fermented cane juice, has a significant volume ranging from 8 to 18 L for every liter of alcohol produced. It contains between 6 and 11% by weight of lignosulfonates, which are essential for the formulation of water-reducing admixture. This study focuses on the characterization of stillage generated at the Santa Cruz rum distillery located in Mayabeque, Cuba, with the aim of assessing its potential as a plasticizer admixture for concrete. Characterization was performed following the Cuban standard NC 228–1 and international references, utilizing Fourier-transform infrared spectroscopy and analyzing parameters such as relative density, total solids, pH, ash content and microbiological characterization. The results indicate the presence of lignosulfonates with plasticizing properties, a low pH that requires neutralization, as well as a moderate solid content and low ash content, suggesting good quality for plasticizing applications. However, the presence of filamentous fungal agents was identified, indicating the need to incorporate biocides in treatment. It is concluded that, with certain modification, stillage can be effectively used in the production of water-reducing admixture.