During extruder processing to manufacture cellulose fiber and film using cellulose-NMMO pre-dope produced by a new method, it seems to occur the changes of molecular weight and ${alpha}$-cellulose content of cellulose upon thermal and mechanical degradation. In an extruder making cellulose solutions from the pre-dope obtained by high-speed mixer, the changes of cellulose molecular weight and ${alpha}$-cellulose content resulted with the variations of processing temperature, concentration of cellulose, and residence time. The molecular weight and ${alpha}$-cellulose content of cellulose decreased with decreasing cellulose concentration and increasing processing temperature. At 15% concentration and short residence time region, the change of ${alpha}$-cellulose content was so high due to high-shear with an increase in temperature. From these processing conditions, the variations of ${alpha}$-cellulose content and molecular weight showed different behaviors, and these processing conditions for making cellulose solution were found to be important factors.