Essential oils are mixtures of secondary metabolites which can be used as additives for food, cosmetic and pharmaceutical industry. Hydro-distillation technique is one of the most common extraction process but optimization studies are quite uncommon. The present study performed a general mass balance concerning the hydro-distillation of Cymbopogon citratus oil in order to determine the input and output currents. the following solute (leaves)-solvent (water) relationships (g/g) were defined: