AbstractCotton linters were hydrolyzed with different concentrations of HCl (2.5-15%) to prepare microcrystalline cellulose. Infrared spectroscopy and thermal analysis were used to follow the effect of hydrolysis on the molecular structure of the produced microcrystalline cellulose. The loss in weight and the degree of polymerization of the produced hydrolyzed cotton linters were determined. Scanning electron microscope images and x-ray diffraction were also studied for more information about the crystallinity, fiber length, particle size, and shape of the produced microcrystalline cellulose. Water retention value and water absorption were estimated for the hydrolyzed cotton linters to explain the effect of hydrolysis on the amorphous and crystalline part of the hydrolyzed cotton linters. The obtained results showed that the crystallinity index of the hydrolyzed cotton increased by increasing acid concentration and then began to decrease at 15% HCl. Kinetic energy (calculated from thermogravimetric curves) of the hydrolyzed cellulose was higher than that of the untreated cotton linters, and at high acid concentration this activation energy began to decrease.