Cellulose has been demonstrated to be dissolved in 7 wt% NaOH/12 wt% urea aqueous solution pre-cooled to -12 °C, as a result of the formation of inclusion complexes (ICs) associated with cellulose, urea and NaOH. However, this cellulose solution is meta-stable, and IC aggregate could form. In this work, the influences of solvent composition and temperature on the stability of the cellulose ICs in NaOH/urea aqueous solvent system were investigated by dynamic and static light scattering. The stability of cellulose ICs in NaOH/urea aqueous solvent system was firstly enhanced and then lessened with NaOH concentration increasing. The addition of urea slightly enhanced the stability of ICs. Furthermore, the solvent composition had been optimized to reduce the aggregation phenomenon of ICs. The proportion of single cellulose ICs in 9 wt% NaOH/13 wt% urea system increased to 0.96, indicating a stable and better dispersion system of the cellulose ICs. Moreover, temperature exhibited great effect on the IC stability. The molecular weight of cellulose in 9 wt% NaOH/13 wt% urea system at 10 °C reached a low value about 7.6×10(4) g/mol and the single cellulose ICs were predominant species in this case. This work provided a better pathway to characterize the dilute cellulose in NaOH/urea aqueous solution, in which the single cellulose ICs were predominant species.