The problem of almost disturbance decoupling is considered for a class of nonlinear systems with unmeasurable time-varying disturbances. A structure, called nested lower triangular form, is introduced, which contains lower triangular form as a special case. The backstepping design technique is applied to construct an H. feedback controller which achieves internal stability of the closed-loop system and renders a bounded L-2 gain from the disturbance input to the output. The application of the developed design method is illustrated through a two continuous stirred tank reactor example, which can be put into the nested lower triangular form. (C) 2003 Elsevier Ltd. All rights reserved.