[en] Nonlinear evolution of collisional drift wave instability is studied numerically. The model equations of quasilinear type are used which describe the modification of background density and the amplitude of unstable drift wave. Their solutions are classified according to the value of a parameter eta which is proportional to the ratio of ion viscous damping to linear growth rate γsub( l). In the vicinity of marginal stability the unstable drift waves are shown to be saturated by flattening of the background density. As eta decreases further we first obtain periodic and later aperiodic solutions. The wave associated diffusion coefficient is obtained numerically as a function of eta and found to be much less than the usual estimate γsub( l)/k sub(perpendicular)sup(2). (auth.)