To improve the convergence property of the iterative dynamic programming (IDP), an adaptive scheme for region size determination is incorporated into the algorithm. In this procedure, IDP is used in multi-pass manner where the initial region over which control candidates are chosen for the next pass is based on the extent of variation of the control variable in the current pass. This procedure, as illustrated and tested with two highly non-linear chemical engineering problems, enables the optimum to be determined more efficiently as compared to the conventional scheme of restoring the region size.