Examination was made of different tensile properties of wet natural cellulose fiber (cotton) and regenerated cellulose fibers (rayon filament). Influence of the crystal region and molecular weight on tensile properties was investigated using mercerized and acid hydrolyzed cotton fibers. No influence of crystal region on tensile properties of cotton fiber was found. The effect of moisture regain on the strength and elongation of cotton decreased with decreasing molecular weight. The slope in the plot of tensile properties against moisture regain became negative, when the molecular weight of the cellulose approximated that of rayon. Changes in tensile strength and elongation with wetting may depend mainly on the number of the molecular chain ends in the amorphous region.