Tobacco, like any other crop, retains its capacity to absorb air moisture through all post-harvest stages. The water content of tobacco leaf after curing or shredding, as well as the capacity of the tobacco to absorb moisture from the air, is important in tobacco manufacture due to its effect on tobacco storage and processing. The capacity of tobacco to absorb moisture from air during processing depends largely on plant variety, agricultural practice, and especially on curing, fermentation and post-curing processing. The level of chemical constituents in the tobacco leaf being processed is related to the hygroscopicity or tobacco moisture uptake. Among these constituents, chloride and the reducing sugars are the most important. Spanish flue-cured production has recently increased and, due to the great interest of growers and manufacturers, a series of physical and chemical determinations for leaf quality in relation to varieties and growing areas was made. Reducing sugar values from a series of data obtained on 227 samples of processed flue-cured tobacco and their relation with tobacco hygroscopic equilibrium have been studied. To evaluate the effect of chloride ion, which as is known, is also related to the hygroscopic properties of tobacco, the samples were sorted into six groups according to their chloride ion content and arranged in intervals of 0.10%. The samples attained moisture content equilibrium in a climate chamber where the tobacco samples, previously powdered and dried, had been stored until they reached constant weight. Reducing sugars were determined from the decoloration attained in potassium ferricyanide solution. The linear regression equations and the correlation coefficient were studied. The results show the positive effect of reducing sugars on the hygroscopicity of flue-cured tobacco grown in Spain.