Cellulose was dissolved rapidly in 4.6 wt % LiOH/15 wt % urea aqueous solution and precooled to -10 degrees C to create a colorless transparent solution. C-13-NMR spectrum proved that it is a direct solvent for cellulose rather than a derivative aqueous solution system. The result from transmission electron microscope showed a good dispersion of the cellulose molecules in the dilute solution at molecular level. Weight-average molecular weight (MW), root mean square radius of gyration (< s(2)>(1/2)(Z)), and intrinsic viscosity ([eta]) of cellulose in LiOH/urea aqueous solution were examined with laser light scattering and viscometry. The Mark-Houwink equation for cellulose in 4.6 wt % LiOH/15 wt % urea aqueous solution was established to be [eta] = 3.72 x 10(-2) M-w(0.77) in the M-w region from 2.7 x 10(4) to 4.12 x 10(5). The persistence length (q), molar mass per unit contour length (M-L), and characteristic ratio (C.) of cellulose in the dilute solution were given as 6.1 nm, 358 nm(-1), and 20.8, respectively. The experimental data of the molecular parameters of cellulose agreed with the Yamakawa-Fujii theory of the worm-like chain, indicating that the LiOH/urea aqueous solution was a desirable solvent system of cellulose. The results revealed that the cellulose exists as semistiff-chains in the LiOH/urea aqueous solution. The cellulose solution was stable during measurement and storage stage. This work provided a new colorless, easy-to-prepare, and nontoxic solvent system that can be used with facilities to investigate the chain conformation and molecular weight of cellulose. (c) 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3093-3101, 2006.