A coupling perturbation method is developed for near optimum design of non-linear systems. A scalar parameter ϵ is introduced in annth-order system such that for ϵ ϵ = the system decouples into two (or more) independent low-order sub-systems. By the same procedure ϵ is introduced into the performance index. The near optimal controlu¯is defined as a truncated power series in ϵ. It is shown that each term of the above series can be sequentially obtained by separate sub-system calculations. Thus a considerable saving in computational effort is achieved