Sodium cellulose sulphate (NaCaS), with degree of substitution (DS) of 1.90, was synthesized by reacting samples of cellulose, covering a wide range of average molecular weight, with S03/dimethyl formamide complex. A solution of NaCS in 0.5 M aq. NaCl was studied by solution viscometry, light scattering and membrane osmometry. The solution was dialysed against solvent. The following MarkHouwink-Sakurada equation and relation between the z-average radius of gyration and weightaverage molecular weight, Mw, were established for 7.2 × 10 4 ⩽ M w ⩽ 1.5 × 10 6 at 25° .The NaCS with salt system was analysed according to the theory of linear non-ionic polymers. Flory's viscosity parameter φ is significantly molecular weight dependent. The partially free draining effect and the excluded volume effect were estimated and the former predominated. The unperturbed chain can be regarded as Gaussian and its dimension A was found to be 1.21 × 10 −8 cmand the conformation parameter a was 2.9.