The nonlinear wave propagation characteristics of ion acoustic (IA) solitary waves in a dusty plasma, i.e. dust ion acoustic (DIA) solitary waves in the presence of ionization, collisions of ions with dust grains and with the background neutral gas, have been investigated by employing a reductive perturbation technique. It has been found that the nonlinear DIA wave is governed by Korteweg–de Vries (KdV) equation with a positive or negative linear damping term. It has also been found that the ionization instability leads to the exponential growth of the DIA solitary wave amplitude with time, whereas ion–dust and ion–neutral collisions reduce the growth rate.