Wood cellulose fibers were oxidized by periodate to obtain dialdehyde cellulose (DAC) fibers. The aldehyde group content, degrees of crystallinity and polymerization, and fiber length of treated fibers were characterized. The tensile strength of the test sheets made of treated fibers was also measured. The results show that periodate oxidation significantly increased the aldehyde group content and the dry and rewet tensile strengths of the test sheets. Sulforiation of the oxidized fibers by bisulfite improved the undried fiber water absorbency and the dry and rewet tensile strengths of the test sheets made of sulfortated fibers.