When cellulose was dissolved in N-methylmorpholine N-oxide(NMMO)/water solution without an antioxidant, the degree of polymerization(DP) of cellulose was lowered with dissolution time elapsed due to oxidative degradation. The DP of cellulose was rapidly reduced at elevated temperature. However, the reduction of DP could be somewhat prevented by adding propylgallate as an antioxidant to cellulose solutions. The effect of dissolution time on the physical properties of regenerated cellulose fibers was also investigated. As the dissolution time increased, the birefringence and the degree of ciystallinity of regenerated cellulose fibers decreased. The increase of the dissolution time also led to the reduction of mechanical strength and modulus due to the reduced DP. The infrared spectra of the prepared fibers showed an intermediate character between pulp and viscose rayon. The mechanical strengths and moduli of the cellulose fibers spun from cellulose-NMMO solutions regardless of the addition of antioxidant were greater than those of viscose rayon. It was attributed to a dry-jet/wet spinning technique which was different from the conventional viscose process. This technique made possible the extrusion of cellulose solutions of higher DP and the molecular orientation due to the elongation flow in the air gap. The cross-section of cellulose fiber produced from NMMO solvent system was round type like the high tenacity viscose rayon. The birefringence of the regenerated cellulose fibers was similar to that of high modulus rayon.