Cellulose was dissolved in 6 wt % NaOH/4 wt % urea aqueous solution, which was proven by a C-13 NMR spectrum to be a direct solvent of cellulose rather than a derivative aqueous solution system. Dilute solution behavior of cellulose in a NaOH/urea aqueous solution system was examined by laser light scattering and viscometry. The Mark-Houwink equation for cellulose in 6 wt % NaOH/4 wt % urea aqueous solution at 25 degreesC was [eta] = 2.45 x 10(-2) weight-average molecular weight (M-w)(0.815) (mL g(-1)) in the M-w region from 3.2 x 10(4) to 12.9 x 10(4). The persistence length (q), molar mass per unit contour length (M-L), and characteristic ratio (C-infinity) of cellulose in the dilute solution were 6.0 nm, 350 nm(-1), and 20.9, respectively, which agreed with the Yamakawa-Fujii theory of the wormlike chain. The results indicated that the cellulose molecules exist as semiflexible chains in the aqueous solution and were more extended than in cadoxen. This work provided a novel, simple, and nonpollution solvent system that can be used to investigate the dilute solution properties and molecular weight of cellulose. (C) 2003 Wiley Periodicals, Inc.