The degree of polymerization (DP) and the molecular weight distribution (MWD) play a special role in producing cellulose fiber by using the N-methyl morpholine N-oxide (NMMO) process. In this paper, rheological methods have been used to determine the MWD of cellulose. It is shown that the limiting compliance J⁰_e of cellulose samples increases strongly with the increasing broadness of MWD, and that the polydispersity index ‹τ_W›/‹τ_N› of the distribution of relaxation times can also well characterize the polydispersity of MWD of the cellulose samples. By using Tuminello's method, the cumulative weight distribution C(M) can be calculated from the terminal modulus and the plateau modulus of the cellulose/NMMO solution via 1-[G'(ω)/and G⁰_N]^0.5 (G'(ω) and G⁰_N are the storage modulus and the plateau modulus respectively).